HMISCU8B5 4-20ma wiring question.

[Boyler3]

Cool. Thanks.

 

[Boyler3]

Guys, not to beat this to death but I have been looking at your replies and comparing them to the drawing I had attached. It suddenly occurred to me that I truly do not know where the source power is coming from and in which order the devices are connected. The drawing was to show tech support how JCI normally wires 4-20ma devices. The installed wire is nearly impossible to get to in order to identify what is what.

These are the things I do know for sure. Currently I have a JCI HVAC controller that reads two 4-20ma signals and converts one to Temperature and one to humidity. It currently reads the same thing as the two little Kele LPI-1Cs displays (cut sheet attached). The JCI controller has the ability to source 15VDC but it does not have to be the source. The idea is to remove the two Kele LPI-1Cs and replace them with the HMISCU8B5 which has the two 4-20ma inputs on it. Both Kele LPI-1Cs have their own two wire pair coming to them. A red wire is on positive and a black wire on negative on each. Like I tried to explain before, if I take C13 and C14 to the red wire and the black to C2 then that input works fine all the way around. I can do the same to the 2nd input and it will also work all the way around by itself. The problem is when both inputs at the HMISCU8B5 are wired at the same time.

Does that information change your response? Do I need to 1st identify the power source and the order that the devices are being wired in? Or is there something that can be inferred from the connections at the two soon to be replaced Kele LPI-Cs? My biggest fear is to hurt something in the present configuration. These devices are located in the duct work and above crowded ceilings which are above operating rooms in a Children's Hospital. I can't afford to have an OR go down because of a wiring mishap. Let me know if you still stick by your answer or if not how you would go about doing what I am attempting. Again, I appreciate everyone's help with this.

 

[pasbra]

I keep my answer! It's not dangerous if the inputs are not critical.

 

[Boyler3]

The inputs are critical to the proper control of the OR on the JCI control's system. But I do appreciate your help and I'm going to go with it. Thanks again.

 

[pasbra]

It's critical for control, not for children operation. You have to put the loop in manual, when you change the connexion. Temperature and humidity are often slow process so you have some minutes...

 

[Boyler3]

I'm with you. I'm not worried about temporary loss of control. I'm worried about blowing the power supply or something along those lines.

 

[OkiePC]

Do you have a loop calibrator?

When in doubt, use the meter to verify that you can get a reading from the source. I use a Fluke 707 which has a MEASURE mode that will show a legit value when the power is provided by the source. It also has a MEASURE Loop Power mode that will allow it to provide the power for passive sensor. And it has a source mode that will allow it to act as a 0 to 20mA device in order to prove and calibrate the analog input of the system I am working with.

If you have a loop calibrator or good meter capable of these types of measurements, then using it prior to making any connections should clear up any doubts.

 

[Boyler3]

Appreciate it. I will have to check my model of Fluke. I don't do a whole bunch with 4-20ma signals. I know my Fluke will read 4-20ma but not sure about generating signals and what not.

 

[drbitboy]

fiddled a bit with @pasbra's image:

 

[Boyler3]

Appreciate it.

 

[Boyler3]

Not seeing a difference between the two.

 

[chud]

I dont have to turn my head upside down to view drbitboys image

 

[danw]

I seriously doubt the illustrated 15Vdc power supply will drive loop current through both the loop powered indicator AND the analog input load.

The AI load is 250 ohms (drops 5V at 20mA) and the loop powered indicator is 300 Ohms, so the loop powered indicator will drop 6 volts at 20mA.

That's 11V of IR drop leaving 4V to lift off the transmitters. I've got my doubts the transmitters would even light up.

 

[pasbra]

I seriously doubt the illustrated 15Vdc power supply will drive loop current through both the loop powered indicator AND the analog input load.

The AI load is 250 ohms (drops 5V at 20mA) and the loop powered indicator is 300 Ohms, so the loop powered indicator will drop 6 volts at 20mA.

That's 11V of IR drop leaving 4V to lift off the transmitters. I've got my doubts the transmitters will even light up.

I agree with you, normaly I work with 24 V power supply! We should have more information about transmitter curve to confirm!

 

[Boyler3]

Funny. I'm looking at the power supply stuff right now. Again, I am no electrician or engineer by any means. How are you coming up with those numbers?