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Uwe Langmesser wrote:
Is there a simple relationship between a meters internal resistance and its sensitivity (ohms per volt). Maybe this is trivial but I don't see it. Uwe The higher the resistance, the lower the operating current, but there is no simple formula. You need a current limiting resistor in series with the meter, and a known supply voltage. Start at the maximum resistance, and slowly reduce it till you have a full scale deflection. Disconnect the voltage, then measure the total resistance of the meter and adjustable resistor. Then use Ohm's law to determine the meter's sensitivity. Its simple and only takes a couple minutes to test. Use a low voltage, and it is a good idea to have different variable resistors to put in series. Start with a higher value resistor than you think you need, so you don't damage the meter, and work your way down. I use an expensive, six decade resistor with an adjustable regulated power supply. I can adjust the resistance in steps, from zero ohms to one megohm in one ohm steps. -- We now return you to our normally scheduled programming. Michael A. Terrell Central Florida |
#2
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Uwe Langmesser wrote: Is there a simple relationship between a meters internal resistance and its sensitivity (ohms per volt). ============================ Yes. Couldn't be more simple. It is the internal resistance of the meter divided by the voltage range the meter is set to. When the meter is at full-scale deflection the current flowing through the meter is always (Voltage Range) / (Ohms per Volt). The internal resistance of the meter, on any voltage range, is the resistance of the moving coil plus the series meter-multiplying resistance. --- Reg, G4FGQ |
#3
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Uwe Langmesser wrote: Is there a simple relationship between a meters internal resistance and its sensitivity (ohms per volt). ============================ Yes. Couldn't be more simple. It is the internal resistance of the meter divided by the voltage range the meter is set to. When the meter is at full-scale deflection the current flowing through the meter is always (Voltage Range) / (Ohms per Volt). The internal resistance of the meter, on any voltage range, is the resistance of the moving coil plus the series meter-multiplying resistance. --- Reg, G4FGQ |
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