This is my first post in the forums. I'm a chemical engineer, so please forgive any ignorance I show when I'm over in the instrumentation neck of the woods.
As the thread title already indicates, I need to know whether one can control two circuits with a SPST switch.
For the refrigeration and process compressors of a pilot plant we're building, we've already ordered and received SPST switches to respond to high suction, low discharge and low differential oil pressure. Originally, the switches were all supposed to feed back directly to the PLC, which would handle the upset conditions by switching off the compressor motor starter.
The customer subsequently decided that they'd instead like the switches to be wired directly to the motor starter to directly de-energize the starter coil during upset AND to also send a signal back to the PLC to indicate on the HMI that the switch has tripped. Since we're behind on the project, we're trying to make the changes without too much fuss. Up to this point, we've figured that we'll need to swap out the SPST switches for DPST to do this.
However, the lead times on getting the new switches are pretty long with respect to our current deadline. Plus, the differential oil pressure switches we've found only appear to have SPST varieties, and their connection to the compressor seems to negate any chance of connecting two of them to achieve the desired effect.
So, would it be possible to connect two wires to the input and output contacts on a SPST switch and have them run to different areas of the plant carrying the same signal? It's just a low-current on/off signal, nothing analog, so it seems that this would accomplish goal of making and breaking the two control circuits simultaneously.
I imagine this is NOT best practice, but, if done with care, could it still work? Before I tell the customer about long lead times or that their preferred new system will not fully work, I wanted to ask people that know a lot more than I do about this sort of stuff. I haven't found anything yet that addresses this, so I'll be thankful for any help you guys can provide.
As the thread title already indicates, I need to know whether one can control two circuits with a SPST switch.
For the refrigeration and process compressors of a pilot plant we're building, we've already ordered and received SPST switches to respond to high suction, low discharge and low differential oil pressure. Originally, the switches were all supposed to feed back directly to the PLC, which would handle the upset conditions by switching off the compressor motor starter.
The customer subsequently decided that they'd instead like the switches to be wired directly to the motor starter to directly de-energize the starter coil during upset AND to also send a signal back to the PLC to indicate on the HMI that the switch has tripped. Since we're behind on the project, we're trying to make the changes without too much fuss. Up to this point, we've figured that we'll need to swap out the SPST switches for DPST to do this.
However, the lead times on getting the new switches are pretty long with respect to our current deadline. Plus, the differential oil pressure switches we've found only appear to have SPST varieties, and their connection to the compressor seems to negate any chance of connecting two of them to achieve the desired effect.
So, would it be possible to connect two wires to the input and output contacts on a SPST switch and have them run to different areas of the plant carrying the same signal? It's just a low-current on/off signal, nothing analog, so it seems that this would accomplish goal of making and breaking the two control circuits simultaneously.
I imagine this is NOT best practice, but, if done with care, could it still work? Before I tell the customer about long lead times or that their preferred new system will not fully work, I wanted to ask people that know a lot more than I do about this sort of stuff. I haven't found anything yet that addresses this, so I'll be thankful for any help you guys can provide.
Thanks.