REFLECTOR: CHT monitor

[Scott Derrick]

Yes,  coupling is possible with millivolt signals. I designed and build
a well drilling rig monitor system and had to use shielded singles for
the millivolt signals. The coupling was about 10-20% for a 30ft run.

Scott

Dave Philipsen wrote:
> Douglas Holub wrote:
>> It's the minus (-) wire, and it might get tied to ground inside the
>> RMI (although that's not the way I'd do it.)
>>
>> A thermocouple is like a tiny battery whose voltage changes with
>> temperature. I've been thinking about it, and if I wanted to measure
>> six batteries to see how their voltage changes with temperature, it
>> would be fine to tie all their negative terminals together and
>> measure each positive terminal individually. I wish I had given it
>> some thought before I wired up two double-pole rotary switches for
>> EGT and CHT. It was a pain.
>>
>> The RMI wiring diagram calls for a double-pole rotary switch, so I'd
>> call Ron at RMI first if I were you. I'd be curious to know what you
>> find out.
>>
>> Doug 
> As I see it the problem is that each of these thermocouples which are
> just like a tiny battery only puts out a very small amount of
> voltage.  We're talking millivolts.  In my opinion, when measuring
> such small voltages, it would be better to have a dedicated pair of
> wires going to each thermocouple instead of relying on a common
> ground.  Additionally, there could be some thermocouple-like couplings
> in the ground bus between each of the thermocouples or between all of
> the thermocouples and the measuring instrument.  I think the best way
> would be a dedicated pair for each thermocouple with each pair being
> of the same type of wire and the same length.
>
> Dave Philipsen
> Velocity STD FG
> N83DP
>
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