Split-range Valve sequencing
Split-ranging of Control Valves can be done by following ways:
1. Single common pnuematic signal from Controller: i.e. using a single common pnuematic signal for both Control Valves. This way requires adding Volume Boosters to Control Valves or positioner to at least one Valve because without them as air volume is from a single I/P and is dividing between two CVs, response of Control Valve action will be slower as air volume is dividing. Benchset of each CV can be set separately and calibrated but it is a time-consuming procedure compared to other easier technique available discussed below.
2. Single common electrical signal output from controller: This common electrical signal from controller is fed to two I/P converters placed in series to each other i.e. both get th same electrical signal. Instead of adjusting Benchset of each CV, each I/P can be calibrated as per Valve behaviour requirement. Also, voltage drop in one I/P's electronic circuitry should not exceed a limit which can cause the other I/P to not have its circuitry required voltage available. Also, with HART enabled smart positioners of CVs, multiple addresses of HART devices in series cause address conflicts and very slow function of HART nodes so due to these disadvantages in this technique, the technique discussed below is the most popular way of implementing the split-range sequencing.
3. Controller Dual Outputs: Most popular way to implement CV Split-range sequencing is this one especially where large capacity Control Systems(DCS,PLC etc) with multiple output channel is available. With dual output controller, split-range programming/setting is done within controller software. Each Control Valve gets its unique signal. Benchset of Control Valve does not need to be adjusted nor I/P calibration needs to be done. Programming the Controller outputs is easy and less time consuming compared to CV positioner calibration or I/P calibration.
1. Single common pnuematic signal from Controller: i.e. using a single common pnuematic signal for both Control Valves. This way requires adding Volume Boosters to Control Valves or positioner to at least one Valve because without them as air volume is from a single I/P and is dividing between two CVs, response of Control Valve action will be slower as air volume is dividing. Benchset of each CV can be set separately and calibrated but it is a time-consuming procedure compared to other easier technique available discussed below.
2. Single common electrical signal output from controller: This common electrical signal from controller is fed to two I/P converters placed in series to each other i.e. both get th same electrical signal. Instead of adjusting Benchset of each CV, each I/P can be calibrated as per Valve behaviour requirement. Also, voltage drop in one I/P's electronic circuitry should not exceed a limit which can cause the other I/P to not have its circuitry required voltage available. Also, with HART enabled smart positioners of CVs, multiple addresses of HART devices in series cause address conflicts and very slow function of HART nodes so due to these disadvantages in this technique, the technique discussed below is the most popular way of implementing the split-range sequencing.
3. Controller Dual Outputs: Most popular way to implement CV Split-range sequencing is this one especially where large capacity Control Systems(DCS,PLC etc) with multiple output channel is available. With dual output controller, split-range programming/setting is done within controller software. Each Control Valve gets its unique signal. Benchset of Control Valve does not need to be adjusted nor I/P calibration needs to be done. Programming the Controller outputs is easy and less time consuming compared to CV positioner calibration or I/P calibration.
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