Transmitter

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Navigation: Main Page -> Models -> Control 2 Models


General Description

The transmitter is used to pass a value to a PID block. Its use is not required since a PID can access a tag directly. However, using the transmitter can improve the display of the control logic on a flowsheet and better represent the actual equipment in the field.

Diagram

Models-Controlle2-image001.gif

Inputs and Outputs

Label Required
Optional
Input
Output
Number of Connections Description
Min Max.

Tx

Optional

Out

0

1

The transmitter value.

RAW

Optional

Out

0

1

The transmitter raw value.

Model Theory

The transmitter can be an orphan model; it need not be connected to any other unit operation. Most of the fields in the transmitter model are for dynamic simulation only in the purpose of control system testing.

The transmitter model can be connected to a PID unit by a control link. To connect, use the insert link function, and select the transmitter as the source (Tx variable) and the PID (Meas variable) as the destination. When the connection is made, the transmitter tag will be automatically put into the PID control block.

The calculation of the transmitted value (TxValue) is as follows:

  • Get the measured value
  • Apply the Transform (if any) to the measured value
  • Apply the Filter (if any) to the transformed value ranged by MinV and MaxV.
  • Then apply any Fail.Mode setting
  • Then range the value by MinValue and MaxValue
  • We now have the final output transmitted value (TxValue)

First Order Filter

The first order filter option is only available in a dynamic project. The transmitted value will change from its current value to the measured value by following a first order response curve. A typical curve is shown below:

First Order Response.png

The Transmitted Value for a given timestep is calculated as follows:

[math]Transmitted Value = Current Value + (Measured Value - Current Value)*(1-e^{-dT/Tau}) \,[/math]

where

Current Value = transmitted value when run started/previous step
dT = timestep
Tau = user specified time constant

Data Sections

The default sections and variable names are described in detail in the following tables. The default Transmitter access window consists of one section.

Summary of Data Sections

  1. Transmitter tab - Contains general information relating to the unit.
  2. Info tab - Contains general settings for the unit and allows the user to include documentation about the unit and create Hyperlinks to external documents.


Transmitter Page

Unit Type: Transmitter - The first tab page in the access window will have this name.

Tag / Symbol Input / Calc Description
Common Data on First Tab Page
On Tick Box All of the independent Transmitters will be enabled or disabled using this box.
ShowCnv Tick Box With this option selected, SysCAD will display engineering units for tags such as Spt, Meas, Output, InMin/Max and OutMin/Max. Note that these will only be displayed after SysCAD has completed at least one iteration.
Count Input The number of independent Transmitters required. The default is 1. The user may also change this number at any time. However, the unit will always add new transmitters after existing ones, and it will delete them starting from the last transmitter.
E.g. if you have 5 transmitters set up and you change this to 4, transmitter number 5 will be deleted.
WithFailMode Tick Box Allows the user to simulate transmitter failure and choose what to transmit.
Check Tags Button SysCAD will perform a check on the validity of the tag(s).
Each independent Transmitter has the following layout. The first Transmitter will be displayed on the first page. Each page thereafter displays two transmitters.
Cfg.[Transmitter number]
Name Input The user can give the individual transmitter a name.
MeasTag Input The measured variable, it must be a valid tag name. The user may type the tag in, however it is preferable to use the cut and paste function to avoid any typing errors.
MeasTagValid Output If MeasTag is a valid tag, this will return 1, otherwise it will return 0.
MeasuredValue / MeasVal Output The current value of the measured variable.
Transform None No conversion will be applied. The Measured value and Transmitter value will be the same.
Linear Converts the Measure value based on linear relationship. The Transmitter value is a function of the measured value: Transmitted value = measured value * Xf.Factor + Xf.Bias
Xf.Factor Input Only visible with the Linear Transform option. The multiply factor.
Xf.Bias Input Only visible with the Linear Transform option. The offset constant.
Note: The Filter variables are only relevant for Dynamic simulations. They are not shown in Steady State projects.
Filter This affects the how quickly the transmitted value is converted from the raw value.
None Any change to the measured value will reflected straight away in the transmitted value.
FirstOrder Applies a first order decay to a step change. See First Order Filter.
Flt.TimeConst / Tau Input Only visible with First Order Filter option. Parameter used in calculating the first order decay to a step change..
Note: The Fail set of variables are only visible if WithFailMode has been ticked.
Fail.Mode Use this list box to choose what to transmit if the transmitter has failed.
None The transmitter has not failed and will continue to operate.
Hold Transmit the last reading.
MinVal Transmit MinValue.
MaxVal Transmit MaxValue.
LoVal Transmit Fail.LoValue.
HiVal Transmit Fail.HiValue.
MinVal,Ramp Only relevant in dynamic projects. Linearly change from the current value to MinValue. The ramp rate is (MaxValue-MinValue)/SlewTime.
MaxVal,Ramp Only relevant in dynamic projects. Linearly change from the current value to MaxValue. The ramp rate is (MaxValue-MinValue)/SlewTime.
LoVal,Ramp Only relevant in dynamic projects. Linearly change from the current value to LoValue. The ramp rate is (MaxValue-MinValue)/SlewTime.
HiVal,Ramp Only relevant in dynamic projects. Linearly change from the current value to HiValue. The ramp rate is (MaxValue-MinValue)/SlewTime.
Fail.LoValue Input Value to be used when Fail.Mode = LoVal. Also used with Fail.Mode = LoVal,Ramp.
Fail.HiValue Input Value to be used when Fail.Mode = HiVal. Also used with Fail.Mode = HiVal,Ramp.
Fail.SlewTime Input Only visible in dynamic projects. Ramping time to be used when Fail.Mode includes Ramp. The ramp rate is (MaxValue-MinValue)/SlewTime.
MinValue / MinV Input Minimum Value to be used when ranging the value. Also used when Fail.Mode = MinVal.
MaxValue / MaxV Input Maximum Value to be used when ranging the value. Also used when Fail.Mode = MaxVal.
Output Transmitter Value
TxValue / TxVal Calc The Transmitted Value, after applying Transform, Filter, Fail.Mode logic and Ranging.
Switches None No switches will be displayed.
MinMaxVal Lo and Hi switches will be evaluated and displayed based on MinValue and MaxValue. eg. if exceeds MaxValue, Hi = 1.
LoHiVal Lo and Hi switches will be evaluated and displayed based on LoLimit and HiLimit. eg. if exceeds HiLimit, Hi = 1.
MinMaxVal,Invert Lo and Hi switches will be evaluated and displayed based on MinValue and MaxValue, but inverted. eg. if exceeds MaxValue, Hi = 0.
LoHiVal,Invert Lo and Hi switches will be evaluated and displayed based on LoLimit and HiLimit, but inverted. eg. if exceeds HiLimit, Hi = 0.
LoLimit / LL Input Only visible with LoHiVal and LoHiVal,Invert switch options. Low value to be compared with the Transmitted value.
HiLimit / HL Input Only visible with LoHiVal and LoHiVal,Invert switch options. High value to be compared with the Transmitted value.
Lo Output Indicates low value being transmitted. If low value transmitted, will display 1, unless invert option is chosen, in which case it will display 0.
Hi Output Indicates high value being transmitted. If high value transmitted, will display 1, unless invert option is chosen, in which case it will display 0.
RawTransform None No conversion to the raw input.
AtoD Analogue to Digital conversion. Converts raw value based on Raw.MinValue->Raw.MaxValue range compared to MinValue->MaxValue range. Result will be rounded down to the nearest integer.
Linear Converts raw value based on Raw.MinValue->Raw.MaxValue range compared to MinValue->MaxValue range. No rounding of result.
Raw.MinValue Input Only visible with AtoD and Linear Raw Transform options. Minimum value for the raw input.
Raw.MaxValue Input Only visible with AtoD and Linear Raw Transform options. Maximum value for the raw input.
Raw.Value / RawVal Calc The raw input value after applying Transform. Note: The Raw Transform does not change the MeasuredValue, it only affects the displayed Raw.Value.
PLCAddress Input PLC address or some similar description. For reference /display purposes only.

Adding this Model to a Project

Insert into Configuration file

Sort either by DLL or Group.

 

DLL:

Control1.dll

Units/Links

Control 2: Transmitter

or

Group:

General

Units/Links

Control 2: Transmitter

See Project Configuration for more information on adding models to the configuration file.


Insert into Project

 

Insert Unit

Control 2

Transmitter

See Insert Unit for general information on inserting units.