Meter Multipliers

| No Comments | No TrackBacks
I bought a Simpson 1329 AC voltmeter off of eBay, which had been modified by an outside company. I haven't figured out the details of the modification yet. The meter's face reads from 0 - 1500, FS=500uA and to use an external 3 megohm multiplier.

In this context, a multiplier means a resistor in series with a meter. In current-reading meters, a shunt resistor is used in parallel. Volts = series. Amps = parallel.

The meter didn't come with a multiplier or multiplier resistor. As I don't have a need to measure voltages at 1.5kV, dividing by ten gives me a useful range: 0 - 150VAC.

Now, a FS=1mA meter movement has a resistance of about 50 ohms, so this meter, having a 500uA meter movement has a resistance of 100 ohms. In order to drop most of this 150V, we need to put a 300kohm resistor in series with the meter.

500 uA = 0.000500 A = 0.5 mA

1500V / 500uA = 3,000,000 ohms
150V / 500 uA = 300,000 ohms
15V / 500 uA = 30,000 ohm
1.5V / 500 uA = 3,000 ohms
0.15V / 500 uA = 300 ohms
0.015V / 500 uA = 30 ohms
0.0015V / 500 uA = 3 ohms

Now you know some basics on making voltmeter dividers.

Another caveat: if the meter is a rectified meter like Simpson's Rectifier series, voltage near the bottom of the scale may be inaccurate unless at least 0.4 - 0.7 V appears across the terminals of the meter. This is because the diodes have to be "switched" on, or forward biased.

No TrackBacks

TrackBack URL:

Leave a comment

About this Entry

This page contains a single entry by Kris Kirby published on June 23, 2012 2:32 PM.

Slot-Fed Corner Reflector was the previous entry in this blog.

Finding HBA WWNs under Solaris 8, 9, 10 is the next entry in this blog.

Find recent content on the main index or look in the archives to find all content.