Table of Contents
Advertisement
Chapter 7 Measurement Tutorial
Measurement Techniques and Sources of Error
Settling Time Effects
The meter has the ability to insert automatic measurement settling
delays. These delays are adequate for resistance measurements with less
than 200 pF of combined cable and device capacitance. This is
particularly important if you are measuring resistances above 100 k .
Settling due to RC time constant effects can be quite long. Some precision
resistors and multi-function calibrators use large parallel capacitors
(1000 pF to 0.1 F) with high resistor values to filter out noise currents
injected by their internal circuitry. Non-ideal capacitances due to
dielectric absorption (soak) effects in cables and other devices may have
much longer settling times than expected just by RC time constants.
Errors will be measured when settling after the initial connection and
after a range change. You may need to increase the delay time before a
measurement in these situations (see page 87).
Errors in High Resistance Measurements
When you are measuring large resistances, significant errors can occur
due to insulation resistance and surface cleanliness. You should take the
necessary precautions to maintain a "clean" high-resistance system. Test
leads and fixtures are susceptible to leakage due to moisture absorption
in insulating materials and "dirty" surface films. Nylon and PVC are
9
relatively poor insulators (10
ohms) when compared to PTFE
13
insulators (10
). Leakage from nylon or PVC insulators can easily
contribute a 0.1% error when measuring a 1 M
resistance in humid
conditions.
262
- Quick Links:
- To Measure Resistance
Hide quick links:
Advertisement
Table of Contents
