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Old 7th Oct 2017, 3:26 pm   #1
Sinewave
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Default Loop Calibrator Project

Hello,

Has anyone here ever made their own loop calibrator?

As a project on the side at home, I'd like to make one.

So at the moment just gathering information and resource on one.

Has anyone got any useful information which might assist?

Thanks.
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Old 7th Oct 2017, 4:59 pm   #2
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Default Re: Loop Calibrator Project

What is a loop calibrator?
 
Old 7th Oct 2017, 5:50 pm   #3
Trevor
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Default Re: Loop Calibrator Project

do you mean a 4-20 ma calibrator ? if so then yes
you can do it easily or the hard way what do you need it for
Trev
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Old 7th Oct 2017, 6:34 pm   #4
Sinewave
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Default Re: Loop Calibrator Project

Quote:
Originally Posted by Trevor View Post
what do you need it for
Mostly for driving PLC inputs.

Quote:
Originally Posted by merlinmaxwell View Post
What is a loop calibrator?
It's a handy device for checking/testing/calibrating 4-20mA analogue inputs and sensors.
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Old 7th Oct 2017, 9:10 pm   #5
ex seismic
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Default Re: Loop Calibrator Project

Made one when at work for checking PLCs. Simple two transistor adjustable constant current generator run off a 9v battery. Good enough for gross calibration error checking. I seem to remember it ran out of puff with some PLCs, probably should have used 18v.

gmb
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Old 7th Oct 2017, 9:23 pm   #6
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Default Re: Loop Calibrator Project

I guess something like this would work ok?

It might need a C across the output, but looks good to me.
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Now where on earth did I remove that from?
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Old 8th Oct 2017, 10:02 am   #7
Trevor
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Default Re: Loop Calibrator Project

all you need is a 24 volt supply a 470 resistor a 10 k linear pot and a multi meter on the ma range connect them in series and then measure the loop current using the ma range on your meter the 470 is to limit the shortcircuit current to 40 ma the 10 k pot will allow the current to be varied from 2ma up
very simple to make and use
trev
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Old 9th Oct 2017, 4:18 pm   #8
Herald1360
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Default Re: Loop Calibrator Project

The 10k pot will need to be rated at 4W or more so as not to exceed its current rating. The LM 317 route could well be cheaper if you need new parts.
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