04-05-2012, 01:42 PM
The purpose of the 1meg resistor is twofold.
Firstly,the resistor isolates the point being measured from the the capacitance of the cable and the instrument itself. I am sure I remember reading an article where someone was testing an audio amplifier and was sick of the loud clicks in the speaker every time he made a measurement with his DMM. The solution was to dig out the valve volt meter which reduced the sound level.
Secondly, the combination of the resistor and lead capacitance acts as a low pass filter to prevent r.f. entering the meter and giving false readings.
Al
Firstly,the resistor isolates the point being measured from the the capacitance of the cable and the instrument itself. I am sure I remember reading an article where someone was testing an audio amplifier and was sick of the loud clicks in the speaker every time he made a measurement with his DMM. The solution was to dig out the valve volt meter which reduced the sound level.
Secondly, the combination of the resistor and lead capacitance acts as a low pass filter to prevent r.f. entering the meter and giving false readings.
Al
Tuned for maximum smoke . 
