I have a PXI-2564 16-SPST module and a PXIe-4081 DMM module. Basically, my system consists of a DC power supply that will supply power to 5 small heaters from a single output. In addition to being able to turn the power on or off to an individual heater, I want to be able to scan through the 5 heater channels and get a single current measurement continuously.
My basic attempt at a schematic has been to split the input voltage into 5 unique channel inputs, giving me control of each heater with ch0-com0 through ch4-com4. The current reading is where my confusion comes into play. I only have a single HI and LO lead for the 4081, so how can I measure 5 channels without physically moving the HI lead?
My attempt at this point is to create a 5x1 MUX on the 2564 that goes into the DMM, and then another 5x1 MUX handling the output of the DMM. The idea being at any given time, I would have 4 open and 1 closed relay on each MUX to chose which device I'm measuring. The issue is this then requires 5 more switches to keep the current routed to the heaters while 1 is re-routed through the DMM.
Am I over thinking this? Maybe have the wrong hardware for the job? Any help would be appreciated, as the NI SWITCH documentation contains little on the actual analog connections for Switch/DMM systems other than "Make the analog connections"
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Have you tried something like the following?:
Essentially hard wire 5 relays together to make a mux, and you do that three times. You then can use a precision resistor, and you take a voltage measurement across the resistor and and calculate current. This will allow you to power all 5 boards independently, while being able to measure current one at a time and not power off the heaters. This should take 3 relays per heater for a total of 15 relays.
For example, you can close relay 2 to power a heater, then close relay 3 and 5 to take the measurement across the resistor.
Thanks so much! I think I had the same idea as you at the same time. See below. Does this make sense?
That makes sense to me! To make sure all the current flows through the DMM, you would need to do a procedure where you do the following, but it should work!
Also your drawing is so much better than mine!