Page 1 of 2 12 LastLast
Results 1 to 13 of 25
  1. #1
    Join Date
    Nov 2009
    Location
    karachi
    Posts
    174

    converting 0-10 vdc signal to 4-20 ma signal

    Hi,

    I need to ask if some one has ever converted 0-10vdc signal to 4-20 ma signal.. has anybody tried this my sensor is giving 0-10 vdc output but my controller accepts 4-20 ma signal...

  2. #2
    Join Date
    Aug 2009
    Posts
    2,459
    What is the impedance of the input?

    Can it accept a 0-20ma signal, or only a 4-20ma signal?

  3. #3
    Join Date
    Sep 2006
    Location
    Alaska
    Posts
    462

    Resistor

    On the Johnson AHU controllers they use
    1. You use 250ohm for 5 VDC and 500ohm for 10 VDC
    2. This gives you a 0 to 20 ma signal
    Law Of The Thermostat: He who has the thermostat wins!!!!!

  4. #4
    Join Date
    Nov 2009
    Location
    karachi
    Posts
    174
    only 4-20 ma signal
    Quote Originally Posted by BACnet View Post
    What is the impedance of the input?

    Can it accept a 0-20ma signal, or only a 4-20ma signal?

  5. #5
    Join Date
    Nov 2009
    Location
    karachi
    Posts
    174
    how we have to connect parralel to the volatage terminal coming out from the transducer..normally we have a 4-20 ma signal and if we need to convert it to voltage we use 500 ohm resistance in parallel to the current terminals to convert it inot 2-10 vdc
    Quote Originally Posted by simux View Post
    On the Johnson AHU controllers they use
    1. You use 250ohm for 5 VDC and 500ohm for 10 VDC
    2. This gives you a 0 to 20 ma signal

  6. #6
    Join Date
    Aug 2009
    Posts
    2,459
    Quote Originally Posted by mujtaba12 View Post
    how we have to connect parralel to the volatage terminal coming out from the transducer..normally we have a 4-20 ma signal and if we need to convert it to voltage we use 500 ohm resistance in parallel to the current terminals to convert it inot 2-10 vdc
    It's a whole lot easier to convert a current to a voltage than it is the other way around.

    It would seem that you are saying that you need to scale the signal (0-100% to 20-100%) in addition to changing it from voltage to current. If that truly is the case, you can't just fix everything with a resistor- you're in need of a op-amp circuit of some sort.

  7. #7
    Join Date
    Nov 2009
    Location
    karachi
    Posts
    174
    cant we achieve this by using a simple resistance??in series or in parallel??
    Quote Originally Posted by BACnet View Post
    It's a whole lot easier to convert a current to a voltage than it is the other way around.

    It would seem that you are saying that you need to scale the signal (0-100% to 20-100%) in addition to changing it from voltage to current. If that truly is the case, you can't just fix everything with a resistor- you're in need of a op-amp circuit of some sort.

  8. #8
    Join Date
    Nov 2009
    Location
    karachi
    Posts
    174
    ok suppose if I need 0-10 vdc to 0-20ma then what can I do??[QUOTE=BACnet;11271172]It's a whole lot easier to convert a current to a voltage than it is the other way around.

    It would seem that you are saying that you need to scale the signal (0-100% to 20-100%)

  9. #9
    Join Date
    Aug 2009
    Posts
    2,459
    In a word- No.

    You still haven't given us the impedance information which is the most important thing in this entire thread. Not having seen it though, I can still say that the answer is "No." A resistor network is not going to scale/condition your signal and also boost up the power of the signal enough to achieve 20ma across the input.

    Are you absolutely sure that the board will only read in a 4-20ma signal? What brand makes an analog input that can't be configured?

    If that really is the case, you could always tear out the input resistors (which convert the current signal to a voltage signal that the ADC reads) and replace them with a set that will look at the voltage directly.

    But that would violate all of the certifications for the device and most likely the warranty.

  10. #10
    Join Date
    Aug 2009
    Posts
    2,459
    Quote Originally Posted by mujtaba12 View Post
    ok suppose if I need 0-10 vdc to 0-20ma then what can I do??
    We still need you to tell us the impedance.

  11. #11
    Join Date
    Nov 2009
    Location
    karachi
    Posts
    174
    Its a tac humidity sensor.. I dont know its impedance
    Quote Originally Posted by BACnet View Post
    We still need you to tell us the impedance.

  12. #12
    Join Date
    Aug 2009
    Posts
    2,459
    Quote Originally Posted by mujtaba12 View Post
    Its a tac humidity sensor.. I dont know its impedance
    The input impedance. Of the controller's analog input. That's the information we need to continue this discussion.

    Of course if it's a BACnet controller you can attach the sensor to a better controller (one that can handle other sorts of AI's) and then map the data over to this controller's AI via network writes. Of course you have to set the "Out of Service" property to "true" on the overridden AI to allow it to take the write.

  13. #13
    Join Date
    Aug 2009
    Posts
    2,459
    According to this PDF, TAC humidity sensors can be set to put out 0-10 or 4-20.

    Looks like this is a non-issue...

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event