When a single valve position monitoring device does not provide all the functions required, tandem or even triple mounting one or two additional devices can be the answer.
K Controls distributor in Sweden, Gustaf Fagerberg, has reported that this has been done on a number of emergency shut down valves supplied recently to a leading provider of polyolefins, base chemicals and fertilizers.
Please click on the photograph to enlarge. In this case the partial stroke test device gives valve position feedback via a 4-20mA signal but end of travel limit switches were also required. The K Controls 007 Ex ed certified switchbox can be seen next to the P.S.T. unit.
This approach could also be useful if five or more switch inputs are required or if a positioner does not have all the required position feedback functions.