HP 3457A Service Manual page 212

"ACAL", a 0.5 volt and a 5.0 volt pulse signal is applied to the input attenuators and a measurement is
made to determine the flatness of the signal. For more specific information, refer to the theory of
operation discussion about AC to DC Converter Automatic Calibration. Figure 8-13 illustrates some of
the circuitry used during the Attenuator Flatness Autocal.
Ohms Precharge Amplifier Auto Calibration
The Ohms Precharge Amplifier Autocal is similar to the Ohms Precharge Self Test 9. During Autocal,
16 measurements are made and a calibration constant is determined and placed into RAM, while in the
confidence test a single measurement is made to determine if the readings are within specifications.
Refer to test 9 to determine the circuitry being used during this portion of the ohms auto-cal.
Extended Ohms Range Auto Calibration
The extended ohms range is the 300 Mohm to 3 Gohm range. The Extended Ohms Range Autocal does
not perform a calibration but it does perform a measurement on the 10 Mohm resistance (9.9 Mohm +
100 Kohm) within A2U101 at pin | and checks to determine if the value is 10 Mohm +10%, Should a
failure occur during this "ACAL" procedure, the AUXERR? command will return a value of 512 if
there are no other errors. Figure 8-14 illustrates some of the circuitry used during the Extended Ohms
Range Autocal.
HP 3457A Multimeter
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