Nuts and Volts - September 2010

Insulation Meter Cross Reference

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.1

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Meter Readings Resistance

IDEAS FOR THE FUTURE

Switch contacts get dirty and one way of making sure dirty contacts don’t cause a problem is to solder the switch contacts. Of course, this will dedicate the meter and prevent it from ever being used for anything else.

Replacing the internal batteries when the case is taped together can be a real pain. One idea is to remove the battery and replace it with a soldered-in jumper. Then, there is no internal battery to replace.

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1

2. 5

For those who have real energy, the meter can be backwards engineered and the internal resistors recalculated so the meter can be used on all scales (RX1, RX10, RX100). The resistance scale on the face of the meter will still be off so a cross reference table will be needed, but the meter will be a little more versatile.

5

10

25

50

250 100

100 Ohms

200 Ohms

470 Ohms

1000 Ohms 2 kOhms 4. 7 kOhms 10 kOhms 20 kOhms 47 kOhms 100 kOhms 200 kOhms 470 kOhms

■ FIGURE 9. Cross reference chart.

small enough to fit on the back of the meter, so I just used copious amounts of electrical tape to attach the assembly to the back of the meter.

Ohmmeter

the solder connections need to be protected so they do not move and break.

This assembly of the batteries and pigtail can be put in a plastic chassis box and then attached to the meter. Personally, I never found a commercial box that was both big enough to house the whole battery assembly and

500

Barely moves the meter needle

1 Mohms

2 Mohms

Ohmmeters use Ohm’s Law (Resistance = Voltage ÷ Amperage) to figure out the resistance of the device being measured. The voltage is provided by the meter’s internal battery and remains relatively constant. The amperage is the current through the device being tested; in this case, insulation on wire.

On an analog meter (a meter that has a mechanical meter movement), the needle actually shows the amount of current through the device. It moves to the right as the resistance goes down and the current goes up. When the

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