Performance Considerations; Warm-Up; Autozero - Keithley 2701 User Manual

3-4 Basic DMM Operation

Performance considerations

NOTE

Warm-up

After the Model 2701 is turned on, it must be allowed to warm up for at least two hours to
allow the internal temperature to stabilize. If the instrument has been exposed to extreme
temperatures, allow extra warm-up time.

Autozero

To help maintain stability and accuracy over time and changes in temperature, the
Model 2701 periodically measures internal voltages corresponding to offsets (zero) and
amplifier gains. For thermocouple temperature measurements using the internal reference
junction (i.e., Model 7700 switching module installed), the internal temperature is also
measured. These measurements are used in the algorithm to calculate the reading of the
input signal. This process is known as autozeroing.
When autozero is disabled, the offset, gain, and internal temperature measurements are not
performed. This increases the measurement speed. However, the zero, gain, and
temperature reference points will eventually drift resulting in inaccurate readings of the
input signal. It is recommended that autozero only be disabled for short periods of time.
When autozero is enabled after being off for a long period of time, the internal reference
points will not be updated immediately. This will initially result in inaccurate
measurements, especially if the ambient temperature has changed by several degrees.
NOTE
Remote programming can be used to enable or disable autozero (see Table 3-1).
For maximum system performance, it is recommended that all measurement
cables be limited to less than 3 meters.
To force a rapid update of the internal reference points, set the integration rate
to 0.002 PLC, and then back to the desired rate (i.e., 1.0 PLC). The NPLC
commands to set the integration rate are covered in Section 4.
Model 2701 User's Manual