Pressure Sensor that Inverts a 4-20ma Signal

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Thread Starter

mike mckenna

I'm looking for 1 of 2 things either a 0-5 psi pressure sensor that puts out 20 ma at o psi and 4 ma at 5 psi or a 4-20 ma signal reverser-inverter that would take the 4-20ma and change it to 20-4 ma. this signal is to control a pump that requires 20ma for full speed and modulates to low at 4 ma.

thank you
 
S
There are signal conditioners that would do this, but you could probably get your VFD to interpret the signal that way.

But...depending on the application, you might need a PID controller between the process pressure signal and the pump speed command. It might not work just to feed the process value to the pump as a speed signal (especially if you're trying to maintain a specific pressure).
 
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Mike McKednna

The VFD is built into the motor, grundfos SQE pump, they tell me low ma is lowest speed 20ma is full speed. there is no choice. they have 24vdc input and ground for terminations.

when i reach 0 psi on my sensor i want max speed so i need 20ma or 10v this is the reverse of all the sensors i have found so far. they are all set up to be 0 or 4 ma at 0 psi and 20 at max psi. I'm using this to fill a tank as the tank draws down, lower pressure, i need to speed up the pump. The sensor will have an out put from 4 to about 9ma but the pumps controller needs a signal 20 to 15ma to get the speeds i need. the easiest item would be a reverse signal 5 psi pressure sensor but i have not been able to locate one yet.

thanks for the info i'll look into controller.

thank you
Mike McKenna
 
It sounds like you're measuring tank level using hydrostatic pressure as the operating principle.

You could probably use a 4-20 mA pressure transmitter (with a direct acting signal - increase pressure = increase in mA) together with a proportional-only, single-loop controller with settable "controller action."

However, this will not guarantee a tank level if the load on the system changes.

Good luck!
 
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Mike McKenna

you are correct on the principle i have a digital switch to start and stop the pump. under normal use small water use i want the pump to run as slow as it can to keep the well from drawing down as much. i get much better water. but during high use, irrigation-fire-etc, it will ramp up to full speed. I'm in northern Cal. with droughts and big wild fires. I'll look into the controller and see if that will work.

Thank you
Mike McKenna
 
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