Keithley 2750, Service Manual

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A-4 Accuracy and Optimization Model 2750 Multimeter/Switch System Service Manual
Thus, the actual reading accuracy is 10mV ±36mV or 10.036mV to 9.964mV. Applying
the voltage reading accuracy into the dB equation yields:
Thus, the actual reading accuracy is -60dB + 0.031213dB to -60dB - 0.031326dB.
dBm and dB for other voltage inputs can be calculated in exactly the same manner using
pertinent specifications, ranges, and other reference voltages.
Additional derating factors
In some cases, additional derating factors must be applied to calculate certain accuracy
values. For example, an additional derating factor of 0.02ppm/V must be added to DCV
specifications for voltages over 500V. Before calculating accuracy, study the associated
specifications very carefully to see if any derating factors apply.
Optimizing measurement accuracy
The configurations listed below assume that the multimeter has had factory setups
restored.
DC voltage, DC current, and resistance:
• Select 6-1/2 digits, 10 PLC, filter ON (up to 100 readings), fixed range.
• Use REL on DC voltage and 2-wire resistance measurements.
• Use 4-wire resistance measurements with offset compensation for best accuracy.
AC voltage and AC current:
• Select 6-1/2 digits, 10 PLC, filter ON (up to 100 readings), fixed range.
Temperature:
• Select 6-1/2 digits, 10 PLC, filter ON (up to 100 readings).
dBm 20
10.036mV
10V
--------------------------
log 59.96879dB – = =
dBm 20
9.964mV
10V
-----------------------
log 60.03133dB – = =