1-5 volts to 4-20 ma?

Status
Not open for further replies.
G

Gwow

Newbie level 6
Joined
Feb 20, 2010
Messages
11
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,389
I have a device which expects 4-20 ma commands, but i need to control it with a voltage. What would be the best method for this?

Would this method
https://www.allaboutcircuits.com/vol_3/chpt_8/7.html
be accurate enough with a precision resistor or would something else be required?

Im guessing not, but i dont know exactly which method to pick.
Thanks!
 

There is nothing wrong with this method ..
However, personally I favour circuits that have one of wires “cold” i.e. use common ground ..
Have a look at the attached pdf, circuit nr.2

IanP
:|
 

    G

    Gwow

    Points: 2
    Helpful Answer Positive Rating
Whether to connect the sensing load to ground or not depends on where the supply source comes from. Many sistems use an external Vcc to power the load. Voltages up to 24V may be required if using many loads in series. Nothing wrong if you intend to use only one sensing load. Please also take a look at **broken link removed** and the attached file. You didn´t mention your required precision.
 

    G

    Gwow

    Points: 2
    Helpful Answer Positive Rating
Thanks. I didn't mention precision because i dont really know the precision required. Basically there will be a heater element with about 1 kv on it and there will then be a sine wave riding on it which is controlled by the 4-20ma command (phase angle control, scr). The goal is to produce a linear temperature ramp for the crystal in a vacuum by using a fuzzy controller which can change the sine wave phase and the size of the dc.

How the precision of the phase angle translates to precision in the temperature ramp control i am not sure.

I'll take a look at these and try them out, thanks again!
 

If it is used for sending commands only (digital data) there are no special requirements on precision.
 

The control isn't digital. But the precision requirement is reduced because of the outer temperature controller loop. Besides the 4-20 mA
input range, you should also know if the control input is true isolated or ground referenced (e.g. directly or indirectly connected to
protective earth). In the latter case, only the circuit suggested by IanP would work. Due to the reduced precision requirement, also a
simple series resistor can be sufficient as a V/I converter, if your controller is able to drive 20 mA on output.
 

Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…