[Mini] Wiring instruments in parallel or series?

Tom Parker tom at carrott.org
Sat Mar 19 19:49:16 MDT 2016


On 03/20/2016 07:06 AM, Dr John C Bullas wrote:
> If i want to measure whatever the gauge is measuring in the same way (and
> knowing the range of the resistance over the 0-100 psi or 0-120c range)
> will connecting another earth return wire to the sender, screw up the
> readings?

You cannot connect ohmmeters in parallel because they both supply power to the sender and will get confused by each other's presence. Have a look athttp://www.allaboutcircuits.com/textbook/direct-current/chpt-8/ohmmeter-design/

You should be able to connect a high impedance voltmeter to the sender's signal terminal (either at the sender itself or on the gauge) in parallel with the gauge without significantly affecting the value displayed by the gauge. The voltage measured here will depend on the resistance of the sender (what you want to measure) and the details of the circuit inside the gauge. For example, if you've got the classic mini "on off" voltage stabilizer then you're going to see that on-off in the voltage measured across the sender.

>   https://www.flickr.com/photos/johnbullas/25258092774/
>
> could this just go into the existing earth return wire to the sender?

Probably. You might even find there is a simple relationship between the 
voltage measured and the value displayed by the gauge, but that depends 
on what is inside the gauge.

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