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Anonymous Poster

Pressure Transducer Simulation

11/22/2007 3:46 PM

I've a Motor that have a frequency converter incorporated as part of it.

A pressure transducer ( 4-20 mA / 24VDC) command the motor speed in a centrifugal pump, regarding the pressure of the water piping.

Just to make a dry test in the motor I would like to simulate the pressure variation with a potenciometer (variable resistance).

If somebody can help me to select this variable resistance (power, resistance, etc.) will be very helpful for me.

Thank you.
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uweka
Power-User

Join Date: Jan 2007
Location: Berlin (Germany)
Posts: 332
Good Answers: 1
#1

Re: Pressure Transducer Simulation

11/23/2007 3:17 AM

You must know the input resistance of your unit you want to drive with the 4-20mA signal. Select a DC voltage (24V per example) and calculate the resistor of your potmeter. lets assume your load is 1000 Ohm.

The maximum resistor makes the lowest current (4mA):
Rmax = U / I = 24 / 0.004 = 6000 Ohm
Rpot max = Rmax-Rload = 5000 Ohm
P = 24 *0.004 * 5000 / 6000 = 80mW

The minimum resistor makes the highest current (20mA):
Rmin = U / I = 24 / 0.02 = 1200 Ohm
Rpot min = Rmin - Rload = 200 Ohm
P = 24 * 0.02 * 200 / 1200 = 80mW

So your potmeter has to be 4800 Ohm with a fixed resistor in series of 200 Ohm.

Hope that helps, Regards Uwe

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