Specifications 8
Agilent U1251A/U1252A User’s and Service Guide 157
[1] Input impedance: >1GΩ for 50 mV to 1000 mV ranges. For U1251A, input
impedance is 10 MΩ (nominal) for 5 V to 1000 V ranges. For U1252A, input
impedance is 10 MΩ (nominal) in parallel with 1.1 MΩ at dual display.
[2] The accuracy could be 0.05 %+10 for U1251A and 0.05 %+5 for U1252A. Always
use the NULL function to zero out the thermal effect before measuring the
signal.
[3] The accuracy of 500 Ω and 5 kΩ is specified after NULL function, which is used
to subtract the test lead resistance and the thermal effect
[4] For the range of 50/500 MΩ, the R.H. is specified for <60 %.
[5] The accuracy is specified for <50 nS and after NULL function with open test
lead.
[6] Always use the NULL function to zero out thermal effect with open test lead
before measuring the signal. If the NULL function is not used, add 20 counts to
the DC current accuracy. Thermal effect could occur due to the following:
• Wrong procedures used to measure the high voltage of 50 V to 1000 V for
resistance, diode, and mV measurements.
• After battery-charging has completed.
• After measuring current greater than 440 mA. Thus we recommend that the
meter be left to cool down for a period which is twice the measuring time
used.
[7] Current can be measured up to 10 A continuously. Add 0.5 % to the specified
accuracy if the signal measured is in the range of 10 A to 20 A and for a period
of up to 30 seconds. After measuring current > 10 A, leave the meter to cool
down for twice the measuring time used before application of low current
measurement.
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