Author Topic: How to make the MC050 produce a 4-20mA signal?  (Read 5732 times)

Offline oiltronic

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How to make the MC050 produce a 4-20mA signal?
« on: January 16, 2013, 12:44:35 AM »
How do I connect the MC050 to a valve that requires a 4-20mA input signal?  Is there a standard accepted way to do this?

I've tried connecting a PWM output to a Phoenix signal conditioner, 2-10V in and 4-20mA out, but the signal conditioner doesn't seem to like the MC050's PWM signal.  Is there a signal conditioner that is known to work (converting PWM voltage to 4-20mA), especially so I don't need any intermediate parts?

Failing that, what about a simple RC filter on the PWM output, which still drives a signal conditioner?  Anyone know of a combo that works?

Quax76

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Re: How to make the MC050 produce a 4-20mA signal?
« Reply #1 on: January 16, 2013, 08:17:22 AM »
The MF outputs of the MC050-10 allows you to use it as a current output.
PinConfig: 4 --> 0 - 30000 [0.1 mA]
Your value must be scaled from 40...200 and then connected to "OutputValue"


Offline oiltronic

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Re: How to make the MC050 produce a 4-20mA signal?
« Reply #2 on: January 16, 2013, 07:23:35 PM »
The MF outputs of the MC050-10 allows you to use it as a current output.
PinConfig: 4 --> 0 - 30000 [0.1 mA]
Your value must be scaled from 40...200 and then connected to "OutputValue"

Thanks for the suggestion, but does this actually work for you? Closed-loop PWM mode is used for driving current, and typical 4-20mA inputs have at least a few hundred ohms impedance, so that shouldn't work:

Quote from: Page 18 of the Plus+1 Controller Family Technical Information, 520L0719 Rev KA Nov 2011
In closed loop mode, current is sourced and a constant current is maintained by the module’s operating system using internal current feedback. Load impedance must not exceed 65 ohms.

And page 19 states the minimum current as 10mA, repeatability and absolutely accuracy as 0.5% full scale (0.5/100*3000mA=15mA). So it's very misleading for the software to allow a 0.1mA resolution, when the accuracy is no better than 15mA.

I also recall reading somewhere that this is not recommended for low current values because of the inaccuracy at that range, but I cannot find where that is written. I believe that the current output is intended for driving coils that need power on the order of a hundreds of mA.

Offline Neil

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Re: How to make the MC050 produce a 4-20mA signal?
« Reply #3 on: January 17, 2013, 07:31:15 PM »
Hi

See attached

Neil


jsaluk

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Re: How to make the MC050 produce a 4-20mA signal?
« Reply #4 on: January 30, 2013, 11:57:34 PM »
Axiomatic makes a signal conditioner from PWM to 4-20
Contact at sales@axiomatic.com.
Product group is PWMI-***
Hope that helps

Offline oiltronic

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Re: How to make the MC050 produce a 4-20mA signal?
« Reply #5 on: February 15, 2013, 07:30:25 PM »
I ended up making simple 1k/44uF RC filters between the MC050 MFOUT pin and the signal conditioner (Phoenix 2864163, 100k input impedance).  I used a decent low-noise metal film 1/4W 1k resistor and two 22uF Panasonic EEU-series caps in parallel.  The 'scope showed less than 70mV ripple at 4kHz PWM, 50% duty, much of which, it seemed, was from the input sampling of the signal conditioner itself.  Works great.