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Because, R measurements are made by R to U converting using constant current flowing through R. Voltage converters used in meters have limited resolution 3.5 or 4.5 digits and there is no possibility to obtain the same accuracy when you measure 1MΩ and 1Ω. You don't need to measure 1MΩ with accuracy to 0.01Ω (best resistors have tolerance 0.1% which means 1kΩ during 1MΩ measurement.
If you look at something that not is resistor but has resistance, how can you guess the resistance value of it, for e.g a motor, a transformer ... (coil resistance) or even diode, transistor, Fet ...
Thanks !!!
If you look at something that not is resistor but has resistance, how can you guess the resistance value of it, for e.g a motor, a transformer ... (coil resistance) or even diode, transistor, Fet ...
Thanks !!!
You can measure it, but this is only resistance part (for constant current).
Real coil has wire resistance but has inductance too.
Motor has winding resistance, windings has inductance.
Transformer windings have resistance (different depend on wire gauge).
Diode has dynamic resistance not static for small signal and constant I and U biasing diode (of course, diode has static resistace because semiconductors has resistance but usually that resistance is small and visible onlu for high currents)
rd=dU/dI it changes depend on constant current flowing through diode.
FET - has channel resistance which changes depend on Ugs (gate-source) voltage
if you take a normal ohm meter {like avo etc } and put the + leed on the source of an Ntype fet and the negative lead on the drain
then wet your finger and place across the gate and drain
you should see the resistance from drain the source change dramaticaly on the avo
for a digital meter
most have built in fet tests
so its a matter of a better meter that has the fets sockets and making a set of leads to test other packages using some dil pins and crocks
digital meters will do the same as an avo when used that way
as a quick test
best to use a fet analyzer or build one to test batches for the best device etc....
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