How to convert from Hz to mA.

D

Thread Starter

Dman

Hey guys,

I am in need of your assistance. I am very much a novice of process control. Basically, I have a pump that I would like to use on a basis of mass flow rate. I have an unknown density, making conversion into volumetric flow rate impossible. As such, I have a software program capable of generating a signal in Hz, corresponding to the capacity of the pump motor (0-100%). However, the pump is only capable of accepting an analog input in either amps or volts. As such, I need a way of converting the Hz into amps (4-20mA).

Can you guys help? It would be a amazing to be able to plug a converter in before the pump to solve the problem.

If anyone has any ideas I would really appreciate the help!
 
Check out the frequency to current converters here (or anywhere you happen to be, they're standard devices)

http://www.api-usa.com/signalconditioners_frequency.php

Be aware that
- you need to know your frequency limits, which should be apparent from your flow rate.

- the power needed to drive these. Many are designed for 24Vdc operation, others for 115Vac operation

- 'isolation' costs more, but when you connect devices not powered from the same source the phenomenon of 'ground loop' rears its angry head and can cause problems. Highly recommended, although, sometimes you get lucky with non-isolated connections.
 
M
As I'm sure you know, (but just as background for others) Hz and mA aren't convertible in the same sense that you can convert say degrees Fahrenheit to degrees Celsius. It's like asking to convert pounds to feet.

What it sounds like is that you have pulse generator output that puts out some sort of pulse width modulation (PWM) style output where the signal is high for 100% output and on and off half the time for 50% output.

What you want is some sort of analog signal, like a 4-20 mA or 0-10 vdc output.

There are a lot of way to skin the cat on this... a high tech solution would be to get a simple PLC (there might even be programmable relays) that has a high speed input counter card and a single analog output. Then you simply write a little program that calculates the PWM % based on this, and spits out an analog output signal.

A lower tech solution, which is a bit outside of my area of expertise, might be just building some sort of capacitor and/or op amp device.

If you had a 5 vdc PWM output that was on 50% of the time and you put it through a capacitor filter, you might see that the output voltage is only 2.5 volts. Of course you have delays with this method, compared to using some digital signal processing...

Just my two cents. More information from you will yield more accurate help.

Thanks,

Matt

Colossians 3:23
 
D

Dr. R. Erlich

Happy Thursday,

See Erlich Industrial Development, Corp. (EID, Corp.) OEM Frequency (Hz or KHz) to voltage converter boards at:

http://www.eidusa.com/Interface_Boards_FREQ_VOLT_W_Zero_and_Span.htm

http://www.eidusa.com/Interface_Boards_FREQ_VOLT_W_Direction_Zero_and_Span.htm

http://www.eidusa.com/Interface_Boards.htm

Note: For systems that requires 4-20mA outputs i.e. frequency to 4-20mA converters, use EID’s OEM Voltage to Current transducer:

http://www.eidusa.com/Interface_Boards_4_20_Super_Transducer.htm

http://www.eidusa.com/Interface_Boards_4_20_Scientific_Transducer.htm

http://www.eidusa.com/Interface_Boards.htm

Both industrial interface boards have “Zero” and “Span” adjustments for maximum performance and linearity.

Good luck,

Ron
 
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