# Understanding thermocouple transmitter wiring

I'm trying to use the RMTJ40BD thermocouple (page 12) and I'm having trouble understanding the wiring diagram for the output.

The manual says that Vo and OPG are the outputs but what is OPG, what does the line through Vo and OPG mean and what does the circle with an attachment to ground mean?

• Link to the source of the picture you have embedded please. Feb 4 at 17:31
• probably output ground .... twisted pair, shielded Feb 4 at 17:31
• @Andyaka added! Feb 4 at 17:32
• @jsotola does that mean that I can't tie OPG to A2 ? Feb 4 at 17:34
• the link that you posted is timing out for me Feb 4 at 17:48

Symbol for cables and electrical wiring

It's not identical to what you have but, as far as I can tell, it's saying that the two wires from Vo and OPG are a twisted pair. Furthermore, the dotted line around the pair implies that a screen or shield should be used. So, you need to use shielded twisted pair cable.

I can't tell you what OPG exactly stands for but, for a balanced transmission of a signal from the device, the same impedance should be present in series (and internal) with Vo and OPG and so, you should not consider connecting OPG to anything else.

Here's another example of the same symbol used taken from this web page: -

See also this stack exchange Q and A entitled "What symbol is this?".

OPG is the output ground. This transmitter is properly isolated- the input section is isolated from the power and the output section, and the output section is isolated from the power.

The diagonal line shows the isolation between input and output (power isolation is not shown).

You can tie the isolated sections together as you like, at a single point each, but generally you would want the thermocouple to be floating (so the junction can be earthed at the tip or not), and you would not want power to flow through signal leads (including OPG).

The dashed circle indicates an earthed shield around the two output wires. Note that it is earthed at the receiver end (only).