24vdc coil & pressure transducers

[CharlesM]

I have 2 - 24vdc coils and 3 0-10vdc pressure transducers. When I turn on one of the coils I get a 150psi gain on all the pressure readouts. When I turn on the second I get another 150 psi gain on the pressures. (300psi total) Turn them both off and pressures go back to zero.

In the past I have put diodes on the coils for the spike when turning on. But the diodes don't seem to help. My only other idea is to add another 24vdc supply for the coils.

Any ideas?

 

[elevmike]

If your solenoid actions shouldnt effect the pressure, then your probably right. Just as a matter of practice all our instrumantation is on a seperate power supply.

 

[Vic]

Reading the voltage drop

It sounds like the voltage drop in the wires to the solenoids is being sensed by the analog sensor. This will happen if there are any common wires being used for reading the output of the transducer and supplying power to the solenoids or the transducer.


Two wires, usually a shielded cable, should go from the transducer output to the analog sensor. Nothing else should be connected to these wires. This way, the output voltage of the transducer will be exactly the same voltage at the sensor.

 

[keithkyll]

The problem is in your common return line. There is 3 reurn paths to consider:
Transducer, PLC analog input 0 reference, solenoid return.
When you energize a coil, the return line rises a few millivolts.

Use 2 returns to the 24 DC supply.
#1 for the transducer and PLC input - a dedicated common line.
#2 for the solenoids.

This same concept also applies to the positive line.