Fluke 5790A, Operator'S Manual

Page: 75 / 220

Front Panel Operation
Techniques for Reducing Transfer Errors
4
4-27
4. The choices available under the "Adjust the" softkey are DAY, MONTH, YEAR,
HOUR, MINUTE, and SECOND. The softkeys autorepeat if you hold them down.
Press the [^] key to increment, or the [v] key to decrement the selected parameter.
Note
Time is shown in 24-hour format and includes leading zeros. The format is hh:mm:ss
where hh = hours, mm = minutes, and ss = seconds.
5.
Return the rear panel CALIBRATION STORE switch to NORMAL.
6. To clear the clock setting display, press the "DONE Setting Clock" softkey followed
by "DONE With Utils."
4-35. [SPEC] Key
At any time during front panel operation, you can display the uncertainty specification of
the present output of the 5790A by pressing [SPEC]. To return to normal operation, press
the [SPEC] key again. An example of the specification display follows:
add08y.eps
Note
For INPUT 1 OR 2, the specification displayed is the measurement mode
absolute uncertainty specification. For WIDEBAND, the specification
displayed is the total uncertainty including flatness. For the SHUNT input,
no specification is displayed. The days since calibration relates to the
calibration procedure for the active input (Periodic or WIDEBAND).
4-36. Techniques for Reducing Transfer Errors
In making ac-dc transfers for the purpose of determining absolute ac voltage, errors can
come from dc reversal, loading (both cable induced and instrument input), thermal emfs,
changes in mechanical contact, spurious ground currents in the signal leads, and EMI.
Knowing more about these errors can help reduce the amount of time you spend
experimenting and debugging to get the best possible results. Once you are confident that
error sources are minimized, a good practice is to take three measurements. That way, if
one measurement is faulty, it stands out.
4-37. DC Reversal
In measurement mode, the 5790A cancels potential dc reversal errors by chopping its
internal dc reference into a low-frequency square wave. In transfer mode, it is up to you
to correct for dc reversal to meet specifications. Apply one polarity of dc to the transfer
standard INPUT and press the "Ref" softkey, then reverse the input polarity and press the
"Ref Avg" softkey. In this way you establish a reference that consists of the average of
both polarities of the dc input.