input impedance of ±15V DC Analog Panel Meter #4403?

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wnm4
 
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input impedance of ±15V DC Analog Panel Meter #4403?

Post by wnm4 »

The product page for this panel meter is a bit too light on details.
What is its DC input impedance?
https://www.adafruit.com/product/4403

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Re: input impedance of ±15V DC Analog Panel Meter #4403?

Post by adafruit_support_mike »

Most panel meters draw 100uA at full scale deflection. With a 30V range that would put the DC resistance at 300k.

I'll have someone test a unit and check that.

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Re: input impedance of ±15V DC Analog Panel Meter #4403?

Post by wnm4 »

Speaking of missing information, this web page for this meter needs details on its mounting dimensions (such as the expected size of the holes and their relative spacing) should someone actually want to mount this panel meter in a panel.

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Re: input impedance of ±15V DC Analog Panel Meter #4403?

Post by wnm4 »

Have you had any luck measuring the input impedance or getting the panel mounting dimensions?

As for this statement:

"Most panel meters draw 100uA at full scale deflection. With a 30V range that would put the DC resistance at 300k."

I'd hate to base a design on an assumed current draw when, while looking for other sources of an answer to this question, I've found a good number of similar meters that drew different currents at full-scale deflection. Finally, since this particular meter actually only has a no-deflection-to-full-scale deflection (and range) of 15V, by your argument the actual DC resistance would be 150k presuming your assumption about the current is correct. Yes it can swing both ways depending on the direction of the current but so too can every other analog meter, although the ones built for unidirectional readout have stop pins and face panels that get in the way of them being driven backwards. The only range that is relevant is the range that is covered from zero current flow to full current flow; direction of the current does not enter into it.

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Re: input impedance of ±15V DC Analog Panel Meter #4403?

Post by wnm4 »

85C1 Panel Meter Measurements.jpg
85C1 Panel Meter Measurements.jpg (91.62 KiB) Viewed 91 times
These are the measurements (in inches) that I made on one of these meters with my calipers.
My Fluke DMM says the DC input resistance is approximately 30k ohms and that agrees with some voltage/current measurements that I made into the meter.

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