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Main Menu Automation Plant Numbering Max-i Fieldbus
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Plant Numbering SystemThis page is updated August 22nd 2008. It is only available in English.INTELLECTUAL PROPERTY DISCLAIMER |
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General Definitions |
The following general definitions apply to this specification: The word shall indicate a requirement. |
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Abbreviations |
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Introduction |
PNS is a new numbering system for process plants. There are three basic ideas of PNS:
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Background |
Among other things PNS it is based on the following standards:
The hierarchical structure of the various standards is shown below: ![]() NORSOK is divided into systems and equipments like KKS. It also has an Area specification corresponding to the Plant specification of KKS, but it is not a part of the tag code. Note, that the designations of the S88 and S95 standards depend on the way of operation - batch, continuous or discrete. For example, a beverage
manufacturer may have an area with a production unit for continuous mixing that feeds a process cell for batch processing that feeds a production
line for discrete bottling process. However, for a numbering system it is of course very impractical to use different designations in the same
plant. In fact, the only difference between batch, continuous and discrete operation is that the batch size of a continuous process is infinite and
the batch size of a discrete process is fixed. If e.g. the last stage of a batch process has a shutter (slide gate), which makes it possible to put
the material in bags instead of a silo, it is in fact impossible to tell whether the process should be called a process cell or a production line
because it depends on the position of the shutter. In the same way, if a hopper scale (batch) in
e.g. a feed-mill is replaced by a continuous belt weigher it is no longer a process cell but a production unit, and the unit term no longer exist
so all equipment has to be renumbered. Therefore, the designations of PNS are a general useable mix between the three operation modes of S95 and all
the other standards.
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Terms and |
Site. A geographical production site. The name is typical a shortening of the geographical location like e.g. AV for Avedøre. Site is another name for Plant. Enterprise. A collection of one or more sites. The enterprise level is responsible for determining the products to be manufactured, on which sites they will be manufactured, and in general, how they will be manufactured. The enterprise is a part of the S95 standard, but it is not used in PNS. An enterprise specification has no meaning for a numbering system like PNS because there is only one enterprise. Area. An area of a site like a block on a power station. The area specification is typical a number. Process Cell. A logical grouping of equipment, which contains all physical entities required to make a certain product or one or more batches. A process cell may run one or more batches simultaneously. Process cells are defined at operational boundaries in the plant, e.g. where a batch loses its identity because it is mixed with another material or batches or is used in further production. Production Unit. The same as a process cell, but used in S95 for a continuous production. Production Line. The same as a process cell, but used in S95 for a discrete production like a bottling process. Two of the biggest disadvantages of S95 are the many different terms for the same level and that a unit is not the same as a production unit, which is very confusing. In PNS, production line is used a a common term for process cell, production unit and production line. Train. An individual part of a process cell needed to make one or more parts of a batch. A process cell may have more than one train, and the order of equipment used to make a particular batch is called a Path. Unit. A logical part of a train. A unit is typically centered on a major piece of processing equipment, such as a generator, a boiler, a mixing tank, a reactor, a mill, a pillet press, a silo group etc. In e.g. a feed mill, there may be six units - intake of raw material, weighing and dosing, milling, mixing, pillet pressing and delivery. The unit's primary defining requirement is that it can operate only on a single batch at a time. This does not mean that a batch must be in a single unit. In fact, during material transfers, a batch must be contained in at least two units. The last part of a units is normally a storage elements like a silo, a vessel or a tank, and in many cases they are controlled by their own fieldbus so that an error on one bus does not affect the operation of other units. The units provide the major partitioning of the train equipment. They also are the major structuring elements used in recipes, because the major elements of master and control recipes in the S88 standard are organized as unit procedures. A good way of spotting a unit is by determining if a piece of equipment must run a recipe or needs some information like the silo number in order to operate. If so, it is a unit. If not, it is equipment used by a unit. Working Cell. The same as a unit, but used in S95 for a discrete production. System. The same as a unit. Used in KKS and NORSOK. An example of a KKS system is HFE, which stands for "Air system for solid fuel boiler". Line. A single conveying- processing- or driving line or chain within a unit like e.g.:
Equipment. A single process equipment within a line like a weigher, a conveyor, a valve, a pump, a tank, a pipe etc. Final Control Element. Used in S88 for those type of equipments, which is used to control the process like actuators, sensors, valves, pumps etc. In PNS and most other numbering systems, a final control element is regarded as the same as an equipment. Control Module. A collection of final control elements, which acts as a single entity from a control standpoint like e.g. a control loop that operates via the set point. A control module has a direct connection to the various actuators and sensors. An example of a control module is a pump with flow control. Even though the control module exists in the S88 physical model, not all elements need be physical. For example, the PID controller can be a PLC instruction or DCS object and not a stand-alone device that physically links the flowmeter to the pump. Equipment Module. A collection of control modules, which can carry out a finite number of minor processing activities, i.e., phases. An equipment module is able to receive high level phase commands like e.g. Circulate, Pump-to-Process, Stop, Shutdown etc. and generate high level status messages like Circulating, Pumping-to-Process, Stopped, Shutdown etc. An equipment module runs the same commands regardless of the product. The equipment module is a part of the S88 standard. Function. A single equipment function like a motor current, a tank temperature, a pump pressure, a pipe flow, a start/stop function, the operation status, the operation mode (automatic/semiautomatic/manual) etc. Component. A physical device, which is able to perform one I/O function like a pushbutton with lamp for the start/stop function or a rotary gauge for the operation status. Attribute. A data storage location within a component, which is able to hold one value like configuration and calibration parameters,
error word, vendor ID and type number etc.
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Data Exchange |
One of the most important properties of a modern process control system is the ability to exchange information between different systems and equipment from different manufacturers. This is e.g. one of the main reasons for using fieldbus systems. A modern automation system may consist of three tiers:
There are two standard ways of exchanging information between the different tiers - the Microsoft way and the heterogeneous way. The Microsoft way is based on the object oriented programming model COM, which is the core of DCOM, ActiveX, VBA, OLE, OPC and OPC DA and DX. However, these technologies are only usable on Microsoft platforms and they suffer from a fairly high complexity and great difficulties with different software versions. With COM all pieces of an application has to be deployed at once, so it is not possible to link in new applications dynamically. Besides none of the present Microsoft platforms are true multitasking with a deterministic response time, and they suffer from a continuous degeneration during normal use, so they may not be useable for highly demanding process control. The heterogeneous way is based on the internet standards HTML and XML. HTML is the standard language for displaying information for human
consumption. XML is the standard language for exchanging information for automated consumption. The benefit of HTML and XML is that these
languages are very simple text based languages, which may be used on many different platforms and generated very easily. Unlike traditional method
based systems, XML is self-describing with a name and description for each value and meta data telling how the telegram should be interpreted. It is
therefore not necessary to have an exact number of arguments and to supply them in a precise order, so the various applications may be much looser
coupled than with e.g. DCOM. Because each value has a name, XML fits perfectly together with fieldbus systems using the very efficient
producer/consumer model like Max-i from Innovatic and CAN. On the other hand, all this extra information makes XML extremely inefficient. XML is
hopeless to use directly on e.g. a fieldbus system, but in spite of the very low efficiency, there is no doubt that it is going to be the
future. Many office programs like StarOffice and OpenOffice store their data in XML and even Microsoft is now turning over to XML in their new
.NET technology and in the pro version of Office 2003. In the future, it must be expected that .NET and XML will replace COM and with that, all the
other COM based technologies. Therefore, one of the primary goals of PNS is to make a system, which will enable an unambiguous and loss less conversion
between XML and an efficient fieldbus protocol.
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XML Data |
A typical XML telegram for starting a fan for a solid fuel boiler and reading the hour counter and the number of activations of the fan may e.g. look like this (without any header and meta data):
<siteData>
<siteArea name="Avedoere 3">
<productionLine name="Solid fuel boiler 1">
<equipment name="Fan 101">
<function name="Command 1"
(type="VALUE")
value="01B"
datatype="BOOLEAN"/>
<function name="Time 1"
(type="VALUE")/>
<function name="Number 1"
(type="VALUE")/>
</equipment>
</productionLine>
</siteArea>
</siteData>
The statements in brackets are default and need not to be specified, but even without these statements, this telegram fills approximately 500 bytes plus any header and meta data just for transmitting one Boolean value and asking for two analog values. In a very fast high level Ethernet or FireWire (IEEE 1394) system or internal in a computer this may not be a problem; but for a fieldbus it is of course much too inefficient although the telegram length may be reduced to almost the half by removing most of the space characters. Therefore, a loss less compression algorithm must be found. The first step has already been taken in the above example by combining the Site and Area specification (siteArea). What the first part of the telegram actually does is to transmit the Boolean value 01B to the function: If the possibility in XML for using nested sites, areas, production lines, equipments and functions is not utilized this information may be removed and added later on. This creates a fixed hierarchical structure of:
<siteArea>
<productionLine>
<equipment>
<function
attribute>
This may seem as a limitation, but practical experiences with e.g. DEP and KKS, which are based on a similar fixed structure has shown that this works very well in practice. Complex equipment like a filter may contain several smaller equipments like an air lock, a fan, a cleaning system etc., which could indicate the need for nested equipment, but in such cases, various equipments may just be grouped together by means of a common line number. Some numbering systems like KKS and DEP has a limited possibility for nesting, which makes it possible to number e.g. a motor, a diesel engine or a pump within an equipment. However, if an equipment is so big that it is important to number the various sub-equipments, it is usually also important to communicate with this equipment e.g. for reading the motor current or the pump pressure, but this possibility usually do not exist. It is only possible to access data and signals from the main equipment. If attributes are needed for general data for the production line, the SCADA system must build a "soft" equipment and a "soft" function to hold these "soft" attributes, as it is not allowed to place a function directly under a production line. The name of the soft equipment should be the same as the production line (instead of e.g. Conveyor, Pump etc.). By removing the nesting possibility the following general XML telegram structure is generated:
<siteData>
<siteArea name="[name]">
<productionLine name="[name]">
<equipment name="[name]">
<function name="[name]"
(type="VALUE|ATTRIBUTE-READ|
ATTRIBUTE-WRITE")
(attribute="[0-1023]")
(value="[value]")
(datatype="FIX|FIXBCD|BCD|
FLOAT|BOOLEAN|
TIMESTAMP|ASCII|
RAW")/>
<function name="[name]" ..... />
</equipment>
<equipment name="[name]">
.....
</equipment>
</productionLine>
<productionLine name="[name]">
.....
</productionLine>
</siteArea>
<siteArea name="[name]">
.....
</siteArea>
</siteData>
Parameters in () are optional. Unfortunately, XML is case sensitive, so that e.g. siteArea, SiteArea, sitearea and SITEAREA are not the same. In PNS, it has therefore been defined that all names shall start with a capital letter and all parameter designations like siteArea shall start with a lower case letter. The following letters shall be lower case letters except for the first letter in each part. The various parts should not be separated by means of signs like "-" or "_". Type is used to select between the different telegram types. There are three types of messages as shown below:
The telegram type VALUE is default and need not to be specified. Attribute is used to specify the wanted configuration or calibration parameter in case of an attribute telegram. Datatype is used to specify the data type for the MIS/MES system. The data type for a given attribute may be fixed,
so that the data type should correspond to this type to be able to communicate. This may e.g. be the case in a fieldbus system with simple
devices without microprocessors, but if the SCADA system knows the wanted data type for a fieldbus device it may of course perform any necessary
data conversions. In case of a poll, the data type needs not to be specified.
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Standard Names |
The next step in the compression process is to replace the names for the site, production line, equipment and function with codes exactly in the same way as it is done in most numbering systems. For example, in KKS the long system name "Air system for solid fuel boiler" is replaced with the much shorter "HFE", the equipment name "Fan" is replaced with "AN" and the component name "Pump motor" is replaced with KP. This standardization has the further advantage that it makes any language conversion very easy. If e.g. a system is delivered to Russia and is described with Russian letters in a non-ASCII text string it would be extremely difficult to debug for western personal, but with standard name codes it is possible to select any language without making any changes. In PNS (and most other numbering systems), all codes consist of English Latin capital letters.
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Site and Area |
The site and area is specified by means of two letters for the site followed by a number in the range 1-8 for the area like AV3. The two-letter
code is just a user-defined shortening of the site location like e.g. AV for Avedøre. If PNS is going to be used on a single
area, the site and area specification may be omitted.
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Production Line |
The PNS production line code is a three-letter user-defined code for the name of the production line followed by a number in the range 1-99 like PP1
for pillet press line 1. This is the same as the KKS system code (described later), so that this code may be used.
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Equipment Codes |
The equipment codes of PNS consist of two letters (English capital letters). The letter O is not used since it may be confused with 0. There may also be a possibility for confusion between I and 1, but the most used fonds have a clear difference between the two. The second letter of the equipment code has the following definition:
Group I and U is used for user-defined equipment. The user should define the meaning of the first letter. If the plant is not a nuclear power plant then group N is also free for user-defined equipment. Note that in the following a single letter equipment code refers to this second letter of the two-letter equipment code. The codes for the first letter are shown below. Because group O is not used, the binary code for this is instead used to specify a one-letter code, which only consists of the previously defined second letter. This group always has the name of the main group like F for filters, P for Pumps, T for Tanks etc. It may be used if it is not necessary with a more detailed specification or in case of the Q code, which has no first letter. Any unused codes may be used for user-defined equipment.
In PNS, there is a standard function (described later) for the most common measurement types plus seven empty spaces for user defined values. However, in a process there may be so many special chemicals that this is not enough. This is the reason for the gauge group (G). The user may just use any of the free letters, and then define his/her own function types. The standard functions only apply to the very few standard gauges. Unlike most other numbering systems, it is therefore possible to specify hundreds of different chemicals at the same time and in this way enable easy communication between different automation systems. It is recommended to use the QG (Quality Gauge) as the first choice for chemical analysis and then define the function letters. Actually, the gauge types FG, LG, PG and TG are superfluous as they may be replaced with standard function codes, but they are included anyway to enable a short form numbering without the function code for these very commonly used gauge types.
The code TT (Tank Tray/Tire) is used in case of big columns or tanks, which are (or may be) separated in various trays or tires. Each tray or tire may be regarded as a separate tank, which are vertical serial connected with other tanks to form a column. It is recommended that each column, which is divided into trays or tires, have its own line number, but it may be so big that it instead has each own unit number. The TT code may also be used to enable more than e.g. 16 temperature measurements in a column or tank (described later).
The reason for adding the new letter in front of the
first one is to get a more natural and easy to remember code like e.g. FG
for Flow Gauge, PG for Pressure Gauge, TG for temperature gauge, BC for
Belt Conveyor, CV for control valve, HX for heat exchanger etc.
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Equipment Numbers |
The equipment code is followed by a serial number with the number range 1-999 and an optional suffix letter - A, B or C - to indicate parallel operation. In those cases where the number of similar equipments (same equipment code) do not exceed 9 or 99, it may be practical to base the numbering on a digit hierarchy so that the most significant digit is used to indicate the unit or level like room number 136 on a hotel where the most significant digit (1) very commonly is used to indicate the floor, the middle digit is used to represent the line and the least significant digit is the equipment number. An example of this is shown below with a silo group. ![]() In case of relatively small plants like feed mills etc. with only one production line, the equipment code and number may be enough to identify the equipment. For example in a feed mill, unit 1xx may be used for intake as the example above, unit 2xx for weighing and dosing, unit 3xx for milling, unit 4xx for mixing, unit 5xx for pillet pressing and unit 6xx for delivery. In this way, a very compact and intuitive numbering system is generated. In the above example, the suffix letter is used to indicate parallel shutter valves so that it is easy to tell to which silo a valve belongs. The suffix letter may be very useful in many situations:
The use of the suffix letter is shown below: ![]() In the case with three parallel equipments, the center equipment shall not use any suffix. It is like street numbering. The entry to the main street
does not use a suffix letter, but an entry in the backyard do. If only two units operate in parallel or serial, they shall
use the suffix A and B unless there is one main line and one side line.
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Function Code |
The function code or spare part number is the lowest hierarchical level of PNS. A function may be regarded as a communication channel between all transmitters and all receivers for that function. Most other numbering systems only has an equipment, a sub-equipment or a component specification as their lowest level, but this is not sufficient for communication. For example, it has no meaning to transmit a telegram with the content "Flow gauge number 1", "Push button number 4" or "Tank number 3". What is important is not the flow gauge, the button or the tank, but the actual flow value, the logical signal from the button and e.g. the level and the temperature of the tank. This is also the core of the producer/consumer model and XML. If a gauge has only one value to transmit, it may of course be possible to interpret the name of the gauge as that value. However, a gauge may have many sensors, and e.g. in case of a vortex flow gauge, which calculates the flow by measuring a pressure difference over a limiter orifice, it may also be able to indicate the differential pressure and perhaps the temperature of the medium. All these are functions - not components. Therefore, the most commonly used functions and measuring values like operation command, temperature, pressure, flow, level etc. has been standardized in PNS, so that it is possible to address these functions if a component supports them. The function code consists of one or two letters followed by a number in the range 1-16. One letter is used for standard process values and two letters are used for used defined types. The standard values are:
In case of a two-letter user defined code, the first letter shall not be A, B or C so that the code is not confused with a suffix letter followed by a one-letter code! All values may (also) be Boolean. This is e.g. used in case of limit switches and feedback from the process. If e.g. the feedback signal for a motor comes directly from the motor starter, it should have the function code G. If it comes from a current sensor, the function code should be I, and if it comes from a rotary gauge, it should be R. The function codes are very close to the equipment codes of the widely used ISO 3511 standard (used in e.g. EIS, DEP, KKS and NORSOK) except for a few, minor modifications.
A "-" followed by two letters and three digits is used to indicate a spare part like e.g. HK1-EM020, where EM020 is the spare part number of the electrical motor for HK1. Note that there may be many types of equipment, which use the same spare part, like e.g. HK1-EM020 and P2-EM020. When a spare part number is combined with the equipment number, the part gets a unique component number, which may be used on the drawings. If there are more spare parts of the same type on the same equipment like e.g. more 10 mm bolts, all these get the same number. This way of numbering is more convenient than the traditional serial numbering because there is no longer any need for a cross-reference table between component numbers and spare part numbers. "H" is used (without number) to indicate a hand-operated equipment like 54QV2H for the hand-operated check valve QV2. To be able to use a short form notation without function code the mostly used hand-operated equipment like valves also has a special equipment code (H) as e.g. HV for hand operated valves. This code may be used if it is not necessary with a more detailed type specification. In PNS a negative analog value as e.g. a negative current, a negative power or a negative torque means brake current, brake power or brake torque. It is therefore not necessary with separate brake codes. The two letter codes are user defined. However, it is recommended to use the following standard codes, if these measuring types are used:
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Function Numbering |
The number range for functions is 1-16. This is assumed enough for the majority of equipments except for big columns or tanks, which may have a very high number of temperature measurements. However, in this case the equipment code TT (Tank Tray/Tire) may be used to separate the column or tank in more trays or tires, which can each have 16 temperature measurements. It is also possible to use the user defined function codes T1-T7. In this way, it is possible with up to 80 values of each type if there is no need for any other user-defined functions. The user may select the numbers freely, but if he or she has no preferences it is recommended to use the following standard for the first 4 values:
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Attribute |
The attribute number is new in PNS compared to the other numbering systems. It is included to make it possible to configurate and calibrate the components. For each I/O function, there are 1024 attributes where attribute 0-999 is used for user-defined attributes and the remaining 24 attributes (1000-1023) are used for standard configuration and identification parameters. Many complex equipments like variable speed drives and mass flow gauges typical require 250-500 setup parameters grouped together in logical groups by means of the most significant digit, so for such equipments, the full attribute range is needed. To be able to program the attributes in consumers they must of course have a unique identifier. In practice, this identifier is shared with a
producer, which may be part of the same component like a push buttons with lamp. There is therefore always a producer for each
consumer and the name of the component is identical to the name of the producer. In case of more control panels, the 1024 attributes must be shared
between all producers of the same value. In this way, the attributes can be programmed individually for all components.
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PNS identifier |
PNS is based on alternating numerical digits (n and N) and alphabetical letters (A). The total PNS identifier consist of 80 bits (10 bytes) as shown below:
The Part bit determines whether the PNS number is a part number for the component or a function code for communication with the component. In case of a part number, the last part is the spare part number, so that the total PNS component number is a combination of the equipment number and the spare part number. The spare part number consists of two letters followed by three digits. For the moment, the letter codes have not been defined. The ranges for letters and numbers are: A: A-Z,Æ/Ä,Ø/Ö,Å,Ü,-, b: 0-1, n: 1-8, N: 0-9, nN: 1-16, NNN: 1-999. The binary code for each letter (A) is the ASCII codes A-Z truncated to 5 bits, that is, 00001B for A or a, 00010B for B or b etc. The empty spaces are filled with the Swedish ASCII vowels for the Area and Train specification and filled with the two-letter codes for the function specification. In most cases, the number 0 is not used for functions. Therefore, the binary value 0000 may be regarded as either 0 or 16. In the same way, the
number 000 may represent area 8 instead of 0.
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Max-i Fieldbus |
The function specification may be reduced to a 32-bit or a 16-bit identifier for communication on the Max-i fieldbus as shown below:
The local bit is used to distinguish between local (1) and global (0) signals. Global signals are usually the signals, which shall be consumed by SCADA systems. In this way, a SCADA system can exclude fast local signals so that it will not be overloaded. Because the last letter Z in the equipment code has the binary value 11010B, the equipment codes 111xxB are not used. This is utilized to distinguish between 32-bit and 16-bit addressing. For fieldbus communication, the site and area specification is always omitted, and the production line specification is used to select the fieldbus. It is therefore not necessary to include the production line specification in the fieldbus identifier. Using the production line specification for fieldbus selection is also very appropriate for safety reasons, because an error on a fieldbus for one production line will not influence on other production lines. A production line should be able to work independent of other production lines. The equipment number is placed in front of the fieldbus identifier to let the equipment number determines the telegram priority if PNS is used on
a fieldbus systems like Max-i or CAN, which uses bit-wise bus arbitration.
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Date Types |
The three-bit data type has the following coding:
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FIX and FLOAT |
PNS has two data formats for process values - FIX and FLOAT. Both data formats shall only be used for values, which has been scaled and converted to metric values. If the data are not scaled the data type RAW shall be used instead. For the moment the following standard units has been defined:
The units follow the SI Units (Système International d'unités) except for temperature, pressure, capacitance and work of energy,
where the SI units Kelvin, Pascal, Farad and joule are impractical for process control applications. The temperature is either measured in °C or
°F depending on the country.
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FLOAT |
The FLOAT data type uses the widely used ANSI / IEEE 754 32-bit single-precision floating-point format. This format consists of three parts as shown below.
The sign bit is used to specify the sign of the value. If it is 0, the value is positive, and if it is 1, the value is negative. The mantissa (significand) has two parts: a 1-bit binary integer (also referred to as the J-bit) and a binary fraction. The mantissa is shifted in such a way that the most significant 1 of the binary value becomes the J-bit. This is called normalization. Because the J-bit is always 1, it needs not to be specified. Therefore, it is an implied value in the IEEE single (and double) precision format. The exponent is the power of two needed to correctly position the mantissa to reflect the number's true arithmetic value. To facilitate comparisons among floating-point values it is held in exceee-127 notation, which means that 127 is added to the actual exponent so that the biased exponent is always a positive number. The reason for choosing 127 is that the smallest normalized number can then be reciprocated (1/X) without overflow. Because of the J-bit, the mantissa (without sign) of a normalized value is always greater than or equal to 1 and less than 2. Therefore, it is not possible to represent 0 directly, but if both the exponent and the mantissa is zero then the value is defined to be zero. For very small values, it may not be possible to normalize the value because of the minimum value for the exponent. When the biased exponent is zero, smaller numbers can only be represented by making the J-bit (and perhaps other leading bits) of the mantissa zero. The values in this range are called denormalized (or tiny) values. The use of leading zeros with denormalized values allows smaller values to be represented. However, this denormalization causes a loss of precision. The denormalized values gives a gradual turn over from normalized values to zero, where all the mantissa bits are shifted out to the right by leading zeros. The set of possible data values can be divided into the following classes:
NaNs are used to represent undefined or invalid results, such as the square root of a negative number. The classes are primarily distinguished by the value of the exponent field, modified by the fraction. Consider the exponent and fraction fields as unsigned binary integers:
The two infinities, + and -, represent the maximum positive and negative real numbers, respectively, that can be represented in the floating-point format. Infinity is always represented by a zero mantissa (fraction and J-bit) and the maximum biased exponent. The signs of infinities are observed, and comparisons are possible. Infinities are always interpreted in the affined sense; that is, -infinite is less than any finite number and +infinite is greater than any finite number. Whereas denormalized numbers represent an underflow condition, the two infinity numbers represent the
result of an overflow condition. Here, the normalized result of a computation has a biased exponent greater than 254.
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FIX |
The IEEE floating point format is a widely used standard, but it is very difficult to generate and handle by means of simple low-cost hardware without a microprocessor. There are several reasons for this:
Because of these disadvantages, PNS has the fixed-point data type FIX, which makes it possible for simple hardware based units to generate process values in SI-units. The FIX data type consists of an 18-bit or 26-bit mantissa and a 6-bit exponent as shown below.
The mantissa is a signed, left-shifted, two's-complement, fractional number, with a length of N-bytes plus two bits - usually 18 bits. For an 18-bit mantissa, the number range is -1 to 1 - 217. The exponent is the power of two needed to correctly position the mantissa to reflect the number's true value in SI-units. It is held in excess-23 notation. If the exponent is 23, the value is equal to the mantissa. If the exponent is 24, then the mantissa shall be left shifted one bit, that is, multiplied by two. In the same way, if the exponent is 22, then the mantissa shall be divided by two. The number range for a 6-bit exponent is 2-23 to 240. Because the number range for an 18-bit mantissa is approximately ±1 to ±217, the total number range for a 24-bit FIX number becomes ±2-40 to ±240 or approximately ±0.91×10-12 to ±1.1×1012. In this way, the smallest normalized number can be reciprocated (1/x) without overflow (1/(2-40) = 240). The number range also fit with industrial values where the smallest quantity is typical 1x10-12 (1 pico). Because FIX data are left shifted, it is possible to change the resolution of an A/D converter without informing the receivers. It is even possible for a FIX24 consumer to accept FIX32 data and visa versa - just with a slight loss of accuracy. After commissioning, the exponent is fixed and do not change! It may therefore be implied in e.g. a fieldbus telegram, if the fieldbus can handle 18-bit data like Max-i. In this way, Max-i can transmit any process value with an accuracy of 17 bit plus sign in only two bytes. This saves two bytes compared to the IEEE floating-point format! 17 bit plus sign corresponds to five digits (±99999). This is usually enough for the majority of process values as shown in the table below:
The table shows the absolute state-of-the-art accuracies. The FIX format is extremely efficient for doing digital signal processing. In fact, it is both much faster and gives a higher accuracy than floating-point! This is how it works:
Even though this method is much faster than floating-point arithmetic, it simultaneously has a higher accuracy. A state-of-the-art A/D converter has
a resolution of approximately 24 bits, but with 1.31 fractional arithmetic, all intermediate calculations are done in at least 30 bits (2.30 fraction).
With single-precision floating-point arithmetic in the IEEE 754 format, all intermediate results are rounded to 24 bits.
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Integers |
Signed and unsigned integers do not have their own data type, but use the FIX data type.
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FIXBCD |
The FIXBCD format is similar to FIX with a known/implied exponent, but all data are in BCD (Binary Coded Digit) format, that is, all digits use their own 4-bit nibble with the numbers 0-9. The FIXBCD format is primary intended for numerical displays like 7-segment displays driven directly by a fieldbus controller. Because Max-i has two extra bits, it is possible to handle a standard 4.5-digit display (-199999) with an 18-bit FIXBCD. Like FIX, FIXBCD is left shifted. No matter how many digits are used, the decimal point specification is the same. If e.g. a 6.5-digit
display receives more digits, the extra digits may just be thrown away or used for rounding. If it receives fewer digits e.g. in case of an 18-bit
value, the missing digits may just be shown as 0 or blanked digits.
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BCD |
The BCD format is similar to FIXBCD except that the first nibble is used to specify the decimal point (floating point). If floating point BCD is not
needed, it is recommended to use FIXBCD because of the higher safety and one more digit for a given number of bytes.
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BOOLEAN, |
This data type is used for two-bit Boolean values with or without time stamp. PNS uses two-bit Boolean values, so that four states may be reported. This may be very useful in a lot of cases:
Note that the two bits are just 4 states of the same status - newer two different signals! The data type BOOLEAN is intended to be used together with the fieldbus system Max-i, which is able to transmit a short two-bit telegram. If the data type BOOLEAN is used in an XML telegram, which shall be transmitted, the short telegram is selected. If a telegram with the data type BOOLEAN or TIMESTAMP is received, it is the length of the telegram, which determine, whether the data type is BOOLEAN or TIMESTAMP. For systems, which are not able to handle a two-bit data type, the data type RAW is used for all kinds of groups of bits. In this case, Boolean values are just regarded as a string or group of two bits. A Boolean value with time stamp uses 3 16-bit words as shown below:
Note that the time is counted directly in years (3 least significant digits), months (1-12), days (1-31), hours (0-23), minutes (0-59), seconds (0-59) and milliseconds (0-999). This is only a minor complication of the counter, but it saves many calculations later on. Day=0 is used to indicate an invalid time. The two most significant bits are able to hold one Boolean 2-bit value. The time is always specified in Global Positioning System (GPS) time, which is an atomic time scale used by the GPS system. The benefit of the GPS time is that it is easy to synchronize to and is a continuously increasing time, which is suitable for chronological recording of events down to the microsecond range - even in distributed process plants and big power networks and in ships and aeroplanes, which constantly pass time zones. The GPS time tracks within less than 28 nS with the Coordinated Universal Time (UTC) popularly known as GMT (Greenwich Mean Time) except for an integer number of leap seconds; which are inserted into UTC to keep it within 0.9 seconds of Earth's rotation. The GPS time was zero at 0h 6-Jan-1980 and since it is not perturbed by leap seconds it is now ahead of UTC by 11-12 seconds. At the display time, the time shall be shown in both
GPS time and in local time, that is, compensated for the time zone, any
summer time and the number of leap seconds. The GPS signal contains
information about the number of seconds to subtract to convert the time
to UTC and thereby to local time.
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ASCII |
This data type is used for ASCII text and process values in XML format like e.g.
<function name="MassFlow 1"
value="36.1"/>
Because all XML values are in SI units, the unit for mass flow is implied to kg/s. Note that when data are converted to XML, it is not necessary
to specify the data type to FIX or FLOAT. Like a pocket calculator, an exponent is only used, if the data would otherwise be out of range.
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RAW |
This data type is used for all kind of groups of bits, nibbles, bytes, words or values. Such data usually require a special knowledge for data interpretation and are therefore not directly useable as process values. The data type RAW may e.g. be used for:
Because of the very easy conversion of process values to the FIX format, it is highly recommended not to use the RAW type for normal
process values.
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Automatic |
An important feature of PNS is that it is possible to get a record of all components for e.g. flow gauge A1FG2 just by searching the documentation for this name - without the function code. This may be done fully automatic with any search program! In numbering systems like DEP, which uses the ISO 3511 standard, the use of a gauge is specified by means of letters following e.g. F for flow, P for pressure, L for level, T for temperature and Q for any quality parameter like pH, density, power etc. (not specified). For example, the ISO number #FITBRQCSZA# means a flow indicator (I) and transmitter (T) with a status display (B), a recorder (R) and a totalizer (Q), which is used for control (C), switching (S), trip initiation (Z) and for an alarm (A). It is obvious that this number requires quite a number of bits and a great symbol on the drawing, and if just a small thing is changed like removing the alarm, all documentation, which contains this part, must be rewritten and redrawn. However, it is actually only those equipments, which are not located on the flow transmitter itself, which is of general interest, so most of this information is completely superfluous. It is normal today that a flow gauge has a local indicator and a status display. It may even have a build in recorder etc. With the ISO standard, it is hopeless (with a normal search program) to search the documentation for equipment and components if the use is
not known, because there are so many possibilities.
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Compatibility with |
KKS, DEP and ISO 3511 are so worked in world wide, that it may be impossible to change these numbering systems - even to a better and more
general-purpose alternative. However, a few simple rules make it possible to make an automatic and unambiguous conversion from these systems to PNS.
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KKS Compatibility |
KKS is based on alternating alphabetical letters - A - (English Latin capital letters other than I and O) and numerical digits - N - and is structured in plants, systems and equipment. KKS do not have a function code, but uses XYZ-signals instead as shown below:
The Plant specification of KKS can easily fit into the Site and area specification of PNS. The number ranges for the KKS system specification is exactly the same as the PNS production Line specification, so KKS fit directly into PNS. KKS has an extremely bad utilization of the two-letter equipment codes, which in practice has made it necessary to use the most significant digit of the equipment number as a part of the equipment code like e.g. AA0xx for control valves, AA1xx for shut-off valves, AA2xx for hand operated valves, AA3xx for safety relief valves etc. This is not necessary with PNS, which has shorter and much more intuitive codes for this like e.g. CV for control valve and HV for hand operated valve. In many cases, the two-letter KKS equipment codes contain less information than the second letter alone of PNS! For example, the KKS letter code AT just means any cleaning, drying, filtering and separating equipment. It is not defined whether this is a filter, a screener, a cyclone, a magnet or any other possibility. As a comparison, PNS has 3×26 codes for these types of equipment! In the same way, the KKS code CE just means any electrical measurement. It is not possible to tell whether this is a current, a voltage, a power, a frequency etc. Both KKS and PNS has a suffix letter code for parallel items, but to be able to squeeze the number into a 32-bit value, PNS only has three suffix letters where KKS has a full A-Z letter range. However, because the most significant digit of the PNS equipment numbers are not going to be used as extra equipment codes, this digit may instead be used as a line specification if four parallel lines are not enough. The KKS component code contains a lot of redundant information and is therefore not used very much. Most of the information is also included in the equipment code as e.g. 3GCK10AP001-KP01 where AP001 is pump 1 and KP01 is pump motor 1. It is primary in case of nested equipments like a pump within a pump or a lubrication pump on an equipment that the original KKS component codes are important, but in this case, the most significant digit of the equipment number may be used instead to group various equipments together. This also makes it possible to address functions in both the main equipment and the auxiliary equipments and in this way e.g. measure the lubrication pressure. PNS has two letters and three digits (20 bit) for its component or spare part code, so all KKS component codes (17 bit) may also be used in PNS. In many power stations, a two-letter, two-digits XYZ signal description code is used as a supplement to the KKS component code (KKS do not use X, Y and Z for the first letter). In this code the letters - X, Y or Z - specifies the direction and type of the signal, and the second letter specifies the equipment type as in the KKS component code like e.g. G for a limit switch. However, as in the KKS component code this is usually redundant information since the equipment code already specifies this - except for nested equipment. The real signal information is in the two-digit number. For example, the XYZ code XG03 means greater than low-2, XG01 means greater than low-1, XG02 means greater than high-1 and XG04 means greater than high-2. This meaning is not obvious, so a big description table is needed. The XYZ-signals corresponds to the function codes of PNS. Because the function code of PNS consist of one letter plus one digit and uses two-bit Boolean values it can contain more information than the real two-digit information in the XYZ-signals. It is therefore possible to convert the XYZ-signals to PNS by means of a conversion table and at the same time get a much more intuitive and easy to remember code. In KKS, there are three different measurement codes - C for a direct measurement, F for an indirect measurement and D for the set point for a
closed loop regulator. Previously controllers/regulators was a separate part of the process and therefore had there own (KKS) numbers, and the
process was controlled by discrete inputs and outputs, but today many different equipments has build-in controllers and perhaps a direct
fieldbus interface, which handles all I/O. Therefore a more general purpose scheme is needed. In PNS, this is handled by letting the number
choose between the different possibilities. For example, function number 1 is always the received setpoint in case of a controller.
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DEP Compatibility |
DEP uses three different numbering systems as shown below - one for machine drawings, one for pipe drawings and one for instrumentation and control.
Note that the first letter "P" means three different things - pump, process and pressure! In DEP, the line term is only used on the pipe drawings, but in the machine and instrumentation drawings, the second letter of the unit code may actually be interpreted as a line specification. If the last two digits of the line specification on the pipe drawings are simultaneously regarded as a pipe serial number (equipment number), then DEP comes quite close to PNS. The instrumentation system uses two or three digits for the unit code, but digit number 3 is often equal to the first digit of the equipment number on the machine drawing, so it may be omitted. For example, if pressure transmitter 1 and pump 1 is located in unit 702, then the pressure transmitter is called 702PT001 and the pump is called P7021. DEP has the same problem as KKS. It is possible to combine e.g. a pump (P) and its support equipment like a diesel engine (D) to the code PD, but
again it is extremely seldom that an equipment is driven by so big an engine. If it is, it is more appropriate to specify the engine and the
transmission as separate equipments and use a common line number to connect the equipments. This will enable communication with functions in
both the pump and the diesel engine.
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EIS Compatibility |
The build-up of the EIS code is shown below:
The number of letters in the equipment code depends on the equipment. Electrical equipment has one letter, instrumentation uses two letters - the first two letters of the ISO 3511 standard - and mechanical equipment has three letters. The mechanical code is a simple shortening of the equipment type like COM for compressor. In total, there are less than 60 codes, so the utilization of the three letters is extremely poor compared to PNS, which has 10 times more equipment codes with only two letters. EIS has an A N NN NN specification for area, train, unit and equipment number where PNS has an N AAANN NNN specification for area, production line and
equipment number. As can be seen, EIS easily fit into PNS.
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NORSOK |
In NORSOK there is a different Tag Code for almost all equipment like:
NORSOK do not have the same hierarchical build-up of as the other standards. For example, the tag code does not include an Area specification for dividing the facility, although NORSOK has such a code. NORSOK is therefore not able to handle parallel production lines very well. The system specification is a predefined list of 90 (10-99) systems in the following groups: 00-09: Plant specific (user defined) Because of the lack of hierarchy, the number range for the sequence numbers must be fairly big - up to four digits for pipes. The sequence
numbers shall run consecutively within each system. It is therefore not allowed to put any hierarchical structure into this. This makes it
impossible to convert a NORSOK number to PNS, although the equipment codes of PNS include most of the equipments used by NORSOK.
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PNS Numbering |
A few rules exist when using PNS: For basic equipment like a conveyor, a pump, a flow gauge etc. the site code and area number and the function code may be omitted on the drawings. For example, a pump may have the name A3P1 and the main part of a flow transmitter may have the name A1FG4. Any measuring value, component or equipment is then identified by adding the function code like e.g. A3P1P1 for pressure value 1, A1FG4F1 for flow value 1 and A1FG4U1 for (external) indicator 1. The equipment numbers in each line shall increase in the direction of flow. The most significant digit of the equipment code may be used to specify a line number. If a line is split up in more lines, at least one of the new lines after the splitting equipment should have its own line number. In this way, there will e.g. only be one chain conveyor with shutters in each line, so that it is easy to tell to which conveyor a shutter belongs. The new line number(s) shall start just after the splitting equipment, so that any interconnection pipes, spouts or ducts also gets the new number. Because all parts of splitting equipment have the same line number, the line may be regarded as an equipment module, which may perform high-level functions like Circulate, Pump-to-process etc. If a line is split up in identical lines like e.g. if more pumps are operating in parallel each of these lines shall either have a new line
number or the suffix letter shall be used as explained before. The equipment numbers for the identical lines shall be the same. If there are
more identical parallel production lines the names and numbers of the equipments shall be the same.
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PNS Examples |
A few examples of the PNS numbers without site and area specification are shown below.
A6CE1 = Production line A6, Controller 1
A4P1 = Production line A4, Pump 1
A4P1C2 = Stop button 2
A4P1C3 = Start low speed button 3
A4P1C4 = Start High speed button 4
A4P1C5 = Auto button 5
A4P1C6 = Hand button 6
A4P1C2=00B = Stop command 2
A4P1C3=01B = Start low speed command 3
A4P1C4=11B = Start high speed command 4
A4P1C0 = Received command
A4P1B1=xxB = Actual running status
A4P1U1 = Motor contactor (unit) 1
A4P1G1=xxB = Feed back from motor contactor 1
A4P1Z2 = Circuit-breaker/fuse 2
A4P1R1 = Rotary gauge 1
A4P1R1=xxB = Feed back from rotary gauge 1
A4P1U3 = Local controller (unit) 3
A4P1B3=xxB = OK signal 3 (from controller 3)
C2HK1 = Production line C2, Hammer mill 1
C2HK1C2=00B = Stop command 2
C2HK1C3=01B = Start command 3
C2HK1C0 = Received Command
C2HK1G1 = Feed back from motor starter
C2HK1R3 = Speed Set Point 3
C2HK1R0 = Received Set Point
C2HK1R1 = Actual rotating speed
C2HK1R2 = Speed Difference
C2HK1P1 = Pressure 1 e.g. lubricant
C2HK1T1 = Temperature 1 e.g. motor
C2HK1T2 = Temperature 2 e.g. bearing
C2HK1V1 = Vibration 1
C2HK1V2 = Vibration 2
C2HK1K1 = Operating time (seconds)
C2HK1N1 = Number of startups
C2HK1Z1 = Emergency stop button 1
C2HK1Z2 = Safety stop switch 2
C2HK1A1 = Fire alarm 1
F3AV1 = Production line F3, Distributor valve 1 (multi way)
F3AV1C2=10B = Counter-clockwise start
F3AV1C3=00B = Stop
F3AV1C4=01B = Clockwise start
F3AV1N3=0010..0B = Position command 3 (example)
F3AV1N1=0100..0B = Position status (example)
A3EH1 = Production line A3, Emergency stop 1
A3EH1Z2 = Boolean value 2
E1AG2 = Production line E1, Alarm 2
E1AG2A1 = Fire alarm 1
E1AG2A2 = Fire alarm 2
E1AG2A0 = Summation alarm from equipment
E1AG2Z1 = Alarm acknowledge 1
P8CC1 = Production line P8, Chain conveyor 1
P8GV19 = Production line P8, Shutter 19
with two separate limit switches (A and B)
with the same name
P8TV19 = Production line P8, Two-way valve 19
with combined limit switch
P8GV19C2=01B = Open command 2
P8GV19C3=10B = Close command 3
P8GV19G1=01B = Open from switch A (0xB)
P8GV19G1=00B = Not open from switch A
P8GV19G1=11B = Closed from switch B (1xB)
P8GV19G1=10B = Not closed from switch B
P8TV19C2=01B = Right command
P8TV19C3=10B = Left command
P8TV19C0 = Received command
P8TV19B1=01B = Right status
P8TV19B1=10B = Left status
J9EG1 = Production line J9, Electrical gauge 1
J9EG1I1 = Current 1 e.g. high limit
J9EG1I2 = Current 2 e.g. high-high limit
J9EG1E1 = Voltage 1
J9EG1J1 = Power 1
J9EG1JE1 = Reactive power 1
A3QG1 = Production line A3, pH transmitter 1
with redox and temperature
A3QG1PH1 = pH value 1
A3QG1RX1 = Redox value 1
A3QG1T1 = Temperature value 1
A3QG1T1 = Electrode 1 for temperature 1
A3QG1T2 = Electrode 2 for temperature 2
A3QG1U1 = External indicator 1
L1TG8 = Production line L1, Temperature gauge 8
L1TG8T1 = External thermo element 1
L1TG8T1 = Temperature 1
L1TG8U2 = External indicator 2
L1TG8U3 = External indicator 3
L1TG3T0 = Production line L1, Thermometer without transmitter
L1B1SG1 = Local sight glass 1
L1B1SG2 = Local sight glass 2
L1B1T0 = Local temperature gauge without transmitter
L1B1P0 = Local pressure gauge without transmitter
L4FG2 = Production line L4, Flow Gauge 2 (vortex type)
L4FG2F1 = External restriction orifice for flow 1
L4FG2F1 = Flow 1 e.g. main flow
L4FG2F2 = Flow 2 e.g. high limit
L4FG2U1 = External indicator 1
L4FG2U2 = External recorder 2
S2QH1 = Production line S2, Quality indicator 1
S2QH1PH1 = pH value 1 from SCADA system
S2QH1RX1 = Redox value 1 from SCADA system
K1T23T1 = Production line K1, Tank 23, Temperature 1
K1T23U1 = External indicator 1
K1T22U2 = External indicator 2
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The Living Drawing |
With the suggested number system, it is for the first time possible to expand a simple number on a drawing to a full XML telegram. If e.g. a button with the number AV8SFB2EH104 is pressed this may cause the following telegram in the MIS/MES system:
<siteData>
<siteArea name="Avedoere 8">
<productionLine name="Solid fuel boiler 2">
<equipment name="Emergency stop 104">
<function name="Value 1"
value="01B"
datatype="BOOLEAN"/>
</equipment>
</productionLine>
</siteArea>
</siteData>
Of course, the XML conversion may be done at any time or even be omitted if the receiver understands the PNS codes. In this way, PNS is also very useful with low speed communication channels like a base band telephone line or in an SMS message on a mobile phone. To make a drawing alive in this way is a part of the Innovatic concept "The Living Drawing", which also includes our conveying control system.
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PS! |
This specification is only a first draft. Everybody is very welcome to send any comments and suggestions - e.g. for new equipment or function types. The specification is primary based on experiences from feed mills and heating and power stations so there are without doubt many equipment types missing for other types of plants. We are also very interested in other existing number systems (other than EIS, DEP, KKS and NORSOK). Please send a mail or e-mail to Innovatic. The address is: Innovatic Phone: (+45) 86 84 72 92
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