Assigned new DO Isolated VAC & when testing on false in logic at charm still reading present VAC?

I assigned new SD alarm for a PI and when testing the DO in the logic, everything works as it should. When checking voltage with output is false I still have 120VAC.  

  • You should expect to see 120 VAC across the DO contacts when it is open (Not conducting) as this is the highest impedance in the circuit.

    You see no voltage across the load in this condition. WIth DO energized, the voltage drop should move to the load.

    Andre Dicaire

  • In reply to Andre Dicaire:

    Hello I appreciate your feedback, therefore I am trying to post a pic of the logic for my discussion but I am unable to. May I email it to you?
  • In reply to gbilly :

  • In reply to gbilly :

    Looks like your picture of control studio was posted
  • In reply to Matt Stoner:

    Logic works fine, but physically at the charm I still have voltage
  • In reply to Andre Dicaire:

    At this state I still have voltage present, physically at the charm 120 VAC. 

  • In reply to gbilly :

    Draw out the electrical circuit and indicate where you are taking the measurement. What type of Terminal block are you using? The logic is somewhat irrelevant. If the DO not energized, local yellow LED is off, then the DO channel is not conducting.

    If you have a standard (4 wire) terminal block, with field circuit wired to terminals 1 and 2, then Fused PC power would be connected to terminal 1 and field load connected between terminal 1 and Neutral (External terminal). De-energized CHARM should show full 120 load across terminals of the CHARM.

    However, if you have a Fused Power injected Terminal, the load is connected across the terminals 2 and 4. In this case, with the CHARM deenergized, the 120 VAC should not be seen across the terminals, i.e. the load.

    If you energize the DO in the module and change the state of the CHARM, with yellow LED Lit, you should see a change in the voltage drop, as it moves to the load. Kirchoff's Voltage Law. ( still remember that from college 40 years later, but I don't know where my keys are...)

    Anyway, what you read on the terminals depends on the circuit and where those terminals are located in that circuit. This is a physical field side discussion, not a control module logic discussion. Once the CHARM is confirmed to be working correctly, then your logic will use it.

    Andre Dicaire

  • In reply to Andre Dicaire:

    Most Digital Outputs, CHARMS included, will have some leakage current detected with no load attached.  If you are reading the CHARM with no field wires or load attached, it would not surprise me that you might read voltage with a DVM (Digital Volt Meter).  This leakage current is so small that it does not produce the output to turn on.  

  • In reply to RickV:

    Yes sir, I don't have any field wires terminated yet. I was just testing output using the SD setpoint.
  • In reply to gbilly :

    What RickV said. With no load, you don't have a valid Circuit to troubleshoot. With no circuit, you are indirectly confirming you have a Fused Injected Terminal Block, providing power to the CHARM and you are reading across the non-existent load. The Volt Meter becomes the load I guess and the 120 VAC appears due to leakage current. With a nominal Relay resistance as the load, the voltage divider would push voltage drop across the CHARM rather than Open Terminals with no connected load. Temporarily connect something with at least 250 Ohms. The current draw should remain below 0.5 Amps AC. higher would be better say 500 or 1000 ohms, or an appropriate solenoid.

    Andre Dicaire