How to build a 4-20 mA source for testing?

Are LM317L and LM317LZ the same??

I built one of these (see attached). I haven't used it yet. It will produce a voltage signal, or current.


Will an LM317LZ be suitable (instead of the LM317) for this project?
Just wanted to make sure// Pardon my ignorance..!
 
Constant voltage drop across a known resistor. A 317 regulator has ~ 1.2 Volts between the output and reference so all you need is a resistor to match the current you want.
I don't know how to post a drawing here but send me a PM and I will send one.
Cheers
Roy
 
This is a 'current source' problem from Basic Ohm's Law 101

I use that basic form but you need to integrate the average impedance of the plc to get it to work fine....

I found a bunch of multiturn pot to get more precision and i mounted some in a basic metal outlet box to be my analog simulator. I can either connect it to be sourcing with a jumper to the DC- return or sinking...


I took the design of the sophisticated one and will someday try to make one but is there someone going further and add some features like a display or a ramp generator ?
1 that we got here have the ramp but it is a little bit fast to be usefull and it is not availaible each time i want to use it...I'm stick with my trim pot but it doesn't need battery replacement!
 
Ok Chetts, I have the wrong interface up without the attach option however I found it by clicking the "Go Advanced" button, here's my schematic.

The basic circuit at the top shows how simple it is

I found that some inductive loads tend to oscilate, the fix was adding a small capacitor as shown.
For batteries I use the small transistor type 9V. I tried rechargables once but they were more trouble than they were worth, a pair of batteries last over a year if you remember to turn it off or break the circuit. It can be used without a battery for Transmitter Simulate mode.
The resistor and pot in line with the regulator Out pin set the initial 4 mA (zero)
I may have drawn the zenner backwards but you get the idea it's just for testing the battery so the voltage is not important, anything from 6-12V will do.
The resistor values shown are the sum of fixed plus trim pot, these are calculated values based on 1.25V from Adj to Out, best to set each pot with a good mA meter. I made my calibrator over 25 years ago and never had to adjust the pots, I check occasionally against my Fluke 87
 
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Cheers
Not quite what I was looking for.
Something more challanging like a micro controlled with a LCD & ADC & DAC using some dedicated 4-20mA chips.

Some research found that TI (Texas Instr) makes a few devices that can do the job.
1. XTR110
2. XTR105
3. XTR114

Any one had some success with these?
 
Included in the TI devices is this RCV420.
samples are available too.

RCV420 is a special function IC chip for 4-20mA current loop receiver. It provides complete 4-20mA to 0-5V conversion with 0.1% overall accuracy, 86dB CMR, and more or less 40V common-mode input range. This IC chip is suitable for many applications such as machine monitoring, ESD, RTUs, SCADA, data acquisition, factory automation, industrial and process control.


computer-controlled-4-20mA.PNG

The circuit produces only a 1.5V at a full scale, drop by its internal sense resistance, which is useful in loops containing extra instrument burdens of in intrinsically safe applications where transmitter compliance voltage is at a premium. 10V voltage reference provides a precise 10V output with a typical drift of 5 ppm/°C,which might be very useful for analog-to-digital output conversion. [source : Texas Instruments Application Notes]
 

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