Guildline 6530 Series, Руководство оператора

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Section 3
OM6530-C1-00
19 November, 2019
3-4
3.2. BRIDGE VS DIRECT MEASUREMENT
Two measurement methods are available to perform resistance measurements using a Guildline
6530 High Resistance Bridge-Meter. One method is simply to directly measure the resistance of
the unit under test (UUT) and take the published or previously calibrated long-term measurement
uncertainty of the 6530 High Resistance Bridge-Meter. The second, more accurate, method is to
use the bridge method. In the bridge method, the resistance of the UUT is measured and
compared with and shortly after a known resistance standard has been measured by the same
high resistance meter, as follows.
When using the bridge method always use the best reference resistance standards available to the
operator as the uncertainties of the reference will determine your baseline uncertainty. When
measuring a resistance value using bridge method, you should have both resistors housed in the
shielded enclosure together, to avoid delays waiting for the UUT to stabilize after measuring the
resistance standard. Keep the measurement cycle times longer rather than shorter, as speeding
up a measurement will result in more noise. However, the operator must not take too long a
measurement (too many samples), as this will allow more time for the meter and resistance
standards to drift. A good practice is to take 300 samples using the last 100 for the mean and
standard deviation. The operator must ensure that the resistance standard is calibrated at the
required voltage. Otherwise, the voltage co-efficient must be used when determining the meter
error at voltages other than the calibrated point of the standard, resulting in increased uncertainty.
If the operator changes a measurement parameter such as capacitor or threshold, then the meter
must be re-standardized with a reference resistor. This requirement to maintain the same
capacitor and threshold settings allows for an effective Ratio for UUT:REF of 1:1, 10:1, 100:1,
and in some specific cases can be extended to 1000:1. To maintain these conditions, particular
care should be maintained when working with ratios which are not at 1:1 to keep the ramp time
in the electrometer between 500 millisecond and 1 minute. A list of common test setups as can
be found in the manual in Section 8.2 with the ramp time shown in the Table 8-4. Assuming that
there is negligible environmental variation and that the test parameters are the same, then the
calibrated resistance and the uncertainty of the UUT by the bridge method are characterized by
the following equations (1) and (2):