hello .. can anybody help me to find circuit .. generate 4-20 mA or 0-20 mA
so i can use to test input terminals of PLC
the analog input of the plc have two terminals .. one input and the other terminal is intrnally conected to 24 vdc or ground ... thnx in advance

 

Hey
I once used a chip that converts 0-5v, 0-10V e.t.c to 0-20mA or 4-20mA, its the XTR110KP. Basically at the input side to this chip i had a Potentiometer and the XTR110KP was configured to give 4-20mA output. Really handy device for calibrating and cheap to built. The datasheet shows how to configure it for the above. Also to see what current it was generating just place a multi-meter on current setting inline!
features list here
http://www.chipcatalog.com/TI/XTR110KP.htm

There is a common voltage to current op-amp circuit if you type "voltage to current op-amp" into google there are loads of options, i dont know what output current these circuits provide but should be easy to modify to get what you need!!

 

did u see the attached pic's ..??
i want to test the analog input terminals .. one termianl is internally connected to 24 VDC ! to achieve loop powered ciruit of a transmitter

 

the internal 24vdc can often be jumpered (or switched) out of the input circuit, it is there for transmitter power. also, the ai card can often be configured for 0 - 10 vdc input or 4-20 ma inputs, not sure of your brand. the fluke 787 process meter can do what you are looking for, or a loop controller. or see if you can get your hands on a transmitter. a lot easier then building a drive circuit. or if you have an analog output card...

 

i have a lot of voltage to current converter circuit ... but all consider the load is grounded
i want to circuit to be equivelant for exampl to flow transmitter of loop powered circuit

 

attached is the loop powered 4-20 mA circuit

 

you need a device that is loop powered to generate the 4-20 mA which will connect to th einput of the PLC.
This device will require an input for example a pot to generate a 0-5v signal.

You can look at the TI devices eg. XTR105 & build around that.
Cheers
Chetts

 

How about the simple circuit on the bottom of page 19:

http://www.national.com/ds/LM/LM117.pdf

 

That's a pretty old thread. I'm not sure the OP has any ongoing interest in this one.