Pakscan is Rotork's proprietary two wire, 20mA current loop, actuator control system. The total system comprises a host controller, a Pakscan Master Station, a two-wire loop and Pakscan Field Control Units (FCU) fitted into each actuator. This page relates to the setting of the Pakscan FCU parameters. Check the IQ wiring diagram for Pakscan FCU inclusion.
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Get Settings
Loads the current Pakscan Field Control Unit settings into the page for viewing, editing and saving to file.
Send Settings
Sends the Pakscan FCU settings, as shown on the page, back to the Pakscan. Once sent, these settings will become the settings used by the Pakscan in operation.
Save
Save Pakscan FCU settings, as viewed on the page, to file for future reference.
Load
Previously saved Pakscan FCU files may be loaded into the page for viewing, editing and updating.
Print Screen
Prints the Pakscan FCU to the default Windows printer.
The IQ has four digital inputs labelled Auxiliary 1 to 4. Auxiliary Inputs can be used for actuator control, external indication or a combination of both.
Control Command- hardwired open /closed / stop / ESD control.
External Indication Signal - to forward signals that are external to the IQ, such as tank level switches, pump motor running contacts etc., to the host via the FCU, two-wire loop and master station.
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Each input is individually configurable with regard to its function, a control command or indication signal input, and to the type of input, normally open or normally closed. However, if using the auxiliary inputs are used to command the IQ, each input has a designated function, Aux 1 = open, Aux 2 = close, Aux 3 = stop/maintain and Aux 4 = ESD.
There is a drop down menu which allows easy selection of the input functionality and the input type for each of the four inputs. The menu selection is encoded on the FCU in the form of a binary "mask". The box labelled "Binary" shows this mask in a form similar to what would be read with a Pakscan Paktester Tool. The box labelled "Hex" converts the binary value of the mask into a hexadecimal number as would be seen on the actuator display via the IQ Setting Tool.
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Position Demand
All IQ's have the ability to be commanded both in digital mode (open/stop/close/ESD) and in positioning mode. This box and its associated slider shows the value of the last positioning mode command received by the IQ. Note that if the actuator is used predominantly for open / close duty this command may have been received several days previously.
The value displayed is constantly updated when the page is operating in "run" mode but it cannot be used to send position commands to the IQ, i.e. it is a read only display.Position Feedback
This box and its associated slider shows the position value (0 to 100%) of the IQ. This may be different from the Position Demand box if the actuator has been operated in Digital Mode. The value displayed is constantly updated when the page is operating in "run" mode.
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Motion Inhibit Time
This is the length of time that the motor will wait between stopping and restarting again when sent positioning commands. This timer value has no effect on the time delay between successive digital commands (open, close or stop) being actioned.
Deadband
The control algorithm used for the Pakscan field unit positioner is proportional only. The field unit runs the actuator to the desired position and then stops it. As the actuator and valve combination will have some inertia it is possible that the desired position may be 'overrun' and the positioner will then reverse the actuator direction of travel in order to make the valve adopt the desired position. This phenomenon is termed 'hunting'. The actuator/valve combination may hunt around the control point if the inertia is high. To prevent this from happening there is a Deadband setting whereby once the actuator enters the deadband the motor will be stopped. For example a 5% deadband will cause the motor to be stopped once the actual position is within 5% of the desired position. The inertia will then bring the actual position nearer to the desired position.
It is important to set the deadband such that the actuator does not hunt around the control point.
Hysteresis
In addition to the deadband setting there is also a setting for hysteresis. The field unit positioner will run the actuator until the actual position is within the deadband setting minus the hysteresis setting. This has the effect of instructing the actuator to stop when the position is nearer to the desired position. The actuator will not start again unless the deadband is exceeded. The hysteresis should never be set to a value greater than the deadband.
Valve Travel Timer
This parameter is used to detect situations where the centre column is turning but the drive to the valve has failed. If the field unit detects that the actuator is in motion for a time greater than the setting of the valve travel timer then a VTT alarm bit is set in the IQ alarm block. Exceeding the timer value will not cause the actuator to stop. Although the timer is started as soon as the actuator motor is energised the actuator must be set in Remote for the VTT alarm to be valid.
Position Update Time
The Pakscan system uses a "report by exception" protocol for all digital signals, i.e. only changes of state are reported to the master station. However, with position feedback the position update (in conjunction with position deviation) are used to determine the frequency that position values are relayed to the master station. The position update and position deviation should be set as a pair, setting one without consideration for the other could cause problems with excessive loop traffic leading to slower loop response.
If the IQ's position doesn't change by more than the deviation setting, this timer value will be the frequency that the position will be reported to the master station. This value should be set so as to avoid excessive reporting which in turn will cause more two-wire loop traffic leading in turn to a slower loop response
The recommended minimum value is 10 x loop scan time or 30 seconds, whatever is the greater. If the IQ is being used for Open / Close duty only setting this value and the position deviation to 0 will inhibit the analogue position reporting feature leading to a quicker Pakscan system loop response.
Position Deviation
The Pakscan system uses a "report by exception" protocol for all digital signals, i.e. only changes of state are reported to the master station. However, with position feedback the position deviation (in conjunction with position update time) are used to determine the frequency that position values are relayed to the master station. The position update and position deviation should be set as a pair, setting one without consideration for the other could cause problems with excessive loop traffic leading to slower loop response.
If the IQ's position changes by more than the deviation setting, its new value will be reported to the master station on the next scan. The recommended maximum value is 5%. If the IQ is being used for Open / Close duty only setting this value and the position update time to 0 will inhibit the analogue position reporting feature leading to a quicker Pakscan system loop response.
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The IQ has the ability to have two sets of limit positions. The digital limits are equivalent to the fully open and fully closed positions set during the IQ commissioning stage. The analogue positioning limits are defaulted to the digital limits but can be set to a different set of values, e.g. 10% and 60%. Any position commands received by the FCU will be scaled over this range such that a 50% position command will actually position the IQ to 35%. Note that whatever the limited range positioning values are set to, the IQ will always display the correct position on its LCD.
Low Point
This value determines at what position on the IQ travel a 0% position feedback is sent to the master station. e.g. if this value is set to 10%, and the IQ is anywhere in the region fully closed to 10%, a 0% position feedback will be sent to the master station.
High Point
This value determines at what position on the IQ travel a 100% position feedback is sent to the master station. E.g. if this value is set to 60%, and the IQ is anywhere in the region 60% to fully open, a 100% position feedback will be sent to the master station.
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Torque
Reporting Characteristics
Torque Update Time
The Pakscan system uses a "report by exception" protocol for all digital signals, i.e. only changes of state are reported to the master station. However, with torque feedback signals the torque update (in conjunction with torque deviation) are used to determine the frequency that torque values are relayed to the master station. The torque update and deviation should be set as a pair, setting one without consideration for the other could cause problems with excessive loop traffic leading to slower loop response.
If the IQ's torque value doesn't change by more than the deviation setting, this timer value will be the frequency that the torque will be reported to the master station. This value should be set so as to avoid excessive reporting which in turn will causes more two-wire loop traffic leading in turn to a slower loop response
The recommended minimum value is 10 x loop scan time or 2 minutes, whatever is the greater. If torque values are not required at the master station setting this value and the torque deviation to 0 will inhibit the torque reporting feature leading to a quicker Pakscan system loop response.Torque Deviation
The Pakscan system uses a "report by exception" protocol for all digital signals, i.e. only changes of state are reported to the master station. However, with torque feedback the torque deviation (in conjunction with torque update time) are used to determine the frequency that torque values are relayed to the master station. The torque update and deviation should be set as a pair, setting one without consideration for the other could cause problems with excessive loop traffic leading to slower loop response.
If the IQ's torque changes by more than the deviation setting, its new value will be reported to the master station on the next scan. The recommended maximum value is 5%. If torque values are not required at the master station setting this value and the torque deviation to 0 will inhibit the torque reporting feature leading to a quicker Pakscan system loop response.Torque Filter
This relates to the 8 torque readings taken over the full travel of the actuator. With the filter set to 0 the raw torque data will be fed back to the master station. Filtering allows for an averaging of the latest readings with the historical torque readings. The filter may be set in the range 0 - 255 and gives a torque reading as follows;Reported value =[ new value x ( 1 - (filter factor/256)) ] + [ old value x (filter factor/256) ]
Note on Torque reporting:If torque data is not required for normal use it is recommended that automatic torque data reporting is turned off, i.e. deviation = 0%, timeout = 0 min and filter factor set to the factory default of 127. This will allow for a much faster loop scan time as the loop will not be congested with unwanted torque data. The torque will still be available for collection by the master station / host upon request.
When an IQ actuator is used on a loop controlled by a Pakscan 2 master station fitted with software less than V2.2, automatic torque data reporting must be turned off as the master station is unable to accept torque data.
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Address
Each FCU on a Pakscan loop must have a unique address in the range 1 to 240. This is the device identification that the master station uses to identify which actuator it is talking to. Neither the address not the baud rate can be modified unless the FCU is in loopback and isolated from the master station.
Baud RateThe Pakscan loop baud rate is a function of the Pakscan two-wire loop cable capacitance and resistance. The ideal baud rate value must be calculated using the tables supplied in the Pakscan master station technical manuals. All of the baud rates available are selectable from the drop down menu and all FCU's on the same Pakscan loop must be programmed with the same baud rate. Neither the address not the baud rate can be modified unless the FCU is in loopback and isolated from the master station.
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