21-08-2023, 07:24 AM
All measuring instruments tell lies. Part of good engineering is understanding the lies and working around them.
A DMM will show phantom AC voltages, as will a neon screwdriver and a non-contact voltage detector. At least they are erring on the side of safety. A moving coil meter, with relatively low resistance**, will show low voltage readings in high impedance circuits. The capacitance of a scope probe will give a false impression of high frequencies. And so on.
**Here's an exception. An AVO 8 on the 1000VDC range will present 20M to the circuit. Most DMMs will be 10M.
A DMM will show phantom AC voltages, as will a neon screwdriver and a non-contact voltage detector. At least they are erring on the side of safety. A moving coil meter, with relatively low resistance**, will show low voltage readings in high impedance circuits. The capacitance of a scope probe will give a false impression of high frequencies. And so on.
**Here's an exception. An AVO 8 on the 1000VDC range will present 20M to the circuit. Most DMMs will be 10M.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
