Sanity check please.

I got some meter movements in from eBay. I have no data on them whatsoever.

They are 0-300V DC meters Inside is a series resistor which I have jumped out and a 1n007 to prevent reverse polarity. I wanted to determine the amount of current for full polarity. I placed a 10K 1% resistor in series with the meter which I actually measure at 9.98 ohms.

I measured 8.12 volts from the supply for full deflection. I measured 7.35V across my 10K.

If I am doing my math right ,that is a 735 micro amp meter movement. Or if I use my resistance measurements, 736 micro amps. Am I wrong? Seems a bit high and an odd value for a meter movement.

 

Sounds right to me even though it is an odd value. What value is the original resistor? About 299V across that resistor should come out to the same current.

 

Sanity check please.

I pronounce you sane.

The numbers sound correct to me also. While an odd full scale current it would not surprise me.

Ron

 

Sounds right to me even though it is an odd value. What value is the original resistor? About 299V across that resistor should come out to the same current.

160K ohms. Something isn't adding up. For full deflection of 300V that resistor should be closer to 390K or 300V is going to peg the meter. Unless they planned on having an external trimmer?? It is a 5% resistor which I found odd so maybe that is the deal? An external trimmer?

 

Curiouser and curiouser.
No!
The meter was intended for AC - hence the diode and the lower than expected resistor value.

 

160K ohms. Something isn't adding up. For full deflection of 300V that resistor should be closer to 390K or 300V is going to peg the meter. Unless they planned on having an external trimmer?? It is a 5% resistor which I found odd so maybe that is the deal? An external trimmer?

With the 1N4007 the average voltage is only half of what it would be without the diode.

Also, note that the meter indicates the average current rather than RMS.

Add to that that the average current from a sine wave is 0.637 x peak, as opposed to RMS being 0.707 peak.

 

Also, note that the meter indicates the average current rather than RMS.

Add to that that the average current from a sine wave is 0.637 x peak, as opposed to RMS being 0.717 peak.

But the meter would likely be calibrated (with a 5% resistor??) to indicate RMS value for sine waves.

 

Yes. My explanation is that of why, when considering full wave and RMS in post #4 things don't add up.

I see you hit upon the most significant factor, duty cycle in post #5

 

It is a DC meter. Scale is 300VDC.

No wait. I think it is AC. a sinusoidal symbol over a straight line?