4-20mA supply circuit

Hi everybody
i need a 4-20mA current supply circuit.
i think , if i have 0-10V supply (or tansformator) , i can manage to produce 4-20mA that using suitable resistances..
why i want to this supply,because i want to check analog input cards,.
best regards..

Don't use a transformer. The 4-20 mA signal is DC, and transformers are AC.

The best bet is to use a 24 VDC power supply, two legs of a potentiometer, and a resistor. Calculate the value of the optentiometer and reistor based on Ohm's Law and the resistance of your analog input card. You can then regulate a 4-20 mA current with the potentiometer, powering the loop with the 24 VDC supply.

Anaolg card configurations vary, so look at your manual for proper wiring.

Do you have any analog output card? Then you can get 4 - 20 mA from your analog output card. You can vary the same by giving 25%, 50%, 75%, 100% output.

thank you gents...

Good Idea

Sunith Bakundy said:

Do you have any analog output card? Then you can get 4 - 20 mA from your analog output card. You can vary the same by giving 25%, 50%, 75%, 100% output.

Click to expand...

Thats a pretty good idea... I will have to keep that one in mind.

Here is another. Why not use a meter that is capable of sourcing the 4-20mA signal to the input card? You can also vary 25%, 50%, 75%, 100%.

Just an Idea

Travis

AGENTTINFOIL said:

Here is another. Why not use a meter that is capable of sourcing the 4-20mA signal to the input card? You can also vary 25%, 50%, 75%, 100%.

Just an Idea

Travis

Click to expand...

Many of us use these. I call them "process instruments". The one I use is from Transmation. Google it.

I Agree

I agree with Jimmie. I use an ALTEK 134-2 that will source or read 4-20 ma in ma or percentage. Pricy @ $500 but a good unit.

Leon

4-20 sourcing/ramping

Fluke 787. Great tool for sourcing / ramping.

Another way of generating a 4-20mA signal is to purchase a bag of potatoes and one by one insert them up your anus

The Fluke Process meters are great. I have a 787 and a 789. The 789 provides loop power and a 250 ohm resistor for HART communications. Wonderful for testing a transmitter out in the field or setting up one before the project gets powered up. I hooked up a precision 250 ohm resistor and pass-tru connectors paralleled across the output to provide 0-5 vdc or 0-10 vdc with 2 250's in series. I just plug them into the Fluke and plug the leads into the adapters.

Before I got my first 787, I modified a cheap Dwyer small pressure transmitter that was off calibration. I removed the diaphram and made a screw adustment device out of junk parts. I would use the 24vdc from a SLC500 into the analog input. I used a couple of these for simulations. For long term tests you don't have to worry about batteries going dead.

There are other low cost options for testing current loops, thermocouples, and more, here are examples: http://www.omega.com/ppt/pptsc.asp?ref=CL601_PHCL-602&Nav=a04

http://www.otekcorp.com/otekdwnld/420.pdf

if you are DIY type check this out:

http://forums.mrplc.com/index.php?download=149

Using a 24vdc power supply you could series a 1.2k ohm resistor and a 6k ohm potentiometer (10 turn for better resolution) this will vary the output from 3.8ma to 20ma. And as with analog signal you would feed the series resistors with the positive from the power supply and send the output to the analog input, negative from the power supply to the negative on analog input.

this is what I use

Another one into the hat...


Alaric told me about this little conditioner http://www.actionio.com/products/slimpak2/wv438.html 4-20ma 0-10dc, this and a pot, now you not limited to just ma, use your meter to read and this to source, its a cheep calibrator

The WV438 is a potentiometer input signal conditioner supporting 3-wire potentiometers and slidewire devices from 100 ohms to 100k ohms. The switch selectable output ranges are 0-10VDC,0- 20mA and 4-20mA. All of the output ranges are fully adjustable via pushbutton calibration. The input default range is 0 to 100% of the potentiometer range, but can be adjusted via pushbutton calibration to any 20% portion of the potentiometer. The default output range is 4-20mA.

Click to expand...

Buld your own 4-20mA Simulator

A few years back I was havin a slow month so I decided to build a "good" mA simulator.
After a bit of soldering and a few trips to Radio Shack I nailed it.

Use a LM317 Voltage regulator, 5 ten turn precision resistors, a 5 position rotary switch and a nice small enclosure. The Voltage regulator is the key because it allows you to stay on mark (4,8,12,16, or 20mA) regardless of load resistance.

The unit hooks in series with a 12 - 30 VDC source and can drive a signal into 750R load and stay steady. If you are working with controls 24VDC is usually available or you can gang up 3 9V batteries for a DC source.

I built about 40 of these and sold them for around $150 each in the US and abroad.
Still have a few laying around in the shop... Great to have more than one on hand when setting up and simulating projects.
Look up how voltage regulators operate and you'll figure out how to build your own...