I have a large Weston Station Meter 0-300 VDC made around 1901. Made for a power generation plant, inside of the housing was some sort of mica wafer assembly wired in series with the +binding post. I would assume that this was some sort of resistor, but it is no longer conducting current. Applying just one volt runs the meter to 125V, 3 volts and the needle pegs. Is there an inline resistor I can choose which can be used to make this meter function at line voltage? All I have come up with so far is to use a 6vdc wall wort transformer and some resistors, but surely this was not the way that the meter was set up back when.

 

Does the meter have any small print on the dial to indicate the current corresponding to full-scale deflection?
If not, try applying 1V via a known resistor or two and noting the scale readings, so that the sensitivity can be calculated.

 

Thank you for replying. I used a 1.5v D cell and a 55ohm pot- dialing the pot down a bit, the Weston meter read approx 125v. With no pot, the meter pegs at over 300v with the D battery. I then used a 6 volt wall wart and powered by 22v ac through a powerstat. The wall wart put out about 1volt. That drove the Weston meter to about 125v.

Does the meter have any small print on the dial to indicate the current corresponding to full-scale deflection?
If not, try applying 1V via a known resistor or two and noting the scale readings, so that the sensitivity can be calculated.

 

Thank you for replying. I used a 1.5v D cell and a 55ohm pot- dialing the pot down a bit, the Weston meter read approx 125v. With no pot, the meter pegs at over 300v with the D battery. I then used a 6 volt wall wart and powered by 22v ac through a powerstat. The wall wart put out about 1volt. That drove the Weston meter to about 125v.

You're well on the may to discovering the mA/V specification so you can calculate the value of a replacement multiplier resistor.

You can get high voltage resistors that would be OK for 300V fsd, but its worth using about 3 in series to make the required resistance, to improve safety.

 

I used a 1.5v D cell and a 55ohm pot- dialing the pot down a bit, the Weston meter read approx 125v.

You need to know accurately how much resistance gave you that 125V reading. Use an Ohmmeter to determine that. "Dialing the pot down a bit" is a tad vague .

 

You need to know accurately how much resistance gave you that 125V reading. Use an Ohmmeter to determine that. "Dialing the pot down a bit" is a tad vague .

Generally that won't work.

Take a potentiometer and vary it with a voltage source that gives you 1/2 scale deflection. Measure the voltage across the POT. That should get you the ability to get the current for 1/2 scale.

Take the POT out of the circuit and measure it. That will be the meter resistance,

From there, we can figure out the required series resistance,

 

That is an absolute work of art.

 

That is an absolute work of art.