Voltage Reference - Fluke PM6690 Service Manual

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Timebase Calibration via the GPIB or the USB
The frequency calibration can also be performed by sending
commands over one of the interface buses.
Always end the commands with the Operation Complete
Query * OPC?
Use the following command sequence:
:CAL:ROSC:INIT; * OPC?
:CAL:ROSC:FREQ <num. value>; * OPC? -- select and con-
nect reference frequency --
:CAL:ROSC:START; * OPC?
:SYST:ERR? -- check for errors --
:CAL:ROSC:STOR yyyymmdd --enter calibration date --

Voltage Reference

Although a counter/timer is chiefly an instrument for measur-
ing time and frequency related parameters, this instrument
also has voltage measurement capabilities that you can benefit
from. Under certain circumstances you can do without a
DVM in a test system, but then you have to calibrate and ad-
just the built-in voltage reference regularly to ensure the spec-
ified uncertainty.
Voltage Calibration Procedure
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Test Equipment
You should preferably use a dedicated DC voltage calibrator
with an uncertainty at least a magnitude less than the measure-
ment specification (see Chapter 8 of the Operators Manual).
Alternatively you can use a stable laboratory power supply
with an external precision voltage divider, for instance a
ten-turn potentiometer, in combination with an adequately ac-
curate DVM for verification.
Note: In contrast to a DVM the counter/timer has a wide-
bandwidth input, and the voltage calculation principle
is based on peak-to-peak measurements rather than
mean value or RMS measurements. This means that
HF noise that is often present at the output of standard
calibrators and power supplies must be filtered out
when the test voltages are applied to the counter in-
put. Always use shielded test leads that are as short
as possible.
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Work Instructions
– Arrange your test setup according to the outline given
above.
Note: Both Input A and Input B should be calibrated. If
you want a traceability record you should apply a num-
ber of positive and negative DC voltages covering the
dynamic range and write down the deviations. Use the
following list:
+50 V, +20 V, +5 V, +2 V, +0.5 V, 0 V, -0.5 V, -2 V, -5
V, -20 V, -50 V
– Key in the following sequence on the DUT.
®
USER OPT Calibrate
® ®
Voltage Start Calib
– Follow the step-by-step instructions on the display.
– You must enter a date at the end of the procedure in or-
der to make the result the active user calibration.
– If you want a traceability record, verify the calibra-
tion/adjustment procedure by applying the same list of
voltages as above and write down the deviations.
– Fill out the calibration protocol if required.
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Voltage Calibration via the GPIB or the USB
The following DC voltages should be applied to the
timer/counter in this order: +50, +20, +5, +2, +0.5, 0, -0.5, -2,
-5, -20, -50 V, first to Input A(1) and then to Input B(2).
If you cannot generate the exact voltage, a voltage in the vi-
cinity of the required voltage can be used, but the value must
be sent in the bus command; two values between +50 and
+5 V, seven values between +5 V and -5 V, and two values be-
tween -5 V and -50 V. One value should be near zero.
Always end the commands with the Operation Complete
Query * OPC?
Use the following command sequence, and apply the correct
DC voltage to the specified input before each command:
:CAL:VOLT:INIT; * OPC?
:CAL:VOLT:INP1:VAL 50.0000; * OPC?
:CAL:VOLT:INP2:VAL 50.0000; * OPC?
:CAL:VOLT:INP1:VAL 20.0000; * OPC?
:CAL:VOLT:INP2:VAL 20.0000; * OPC?
*
*
:CAL:VOLT:INP1:VAL -50.0000; * OPC?
:CAL:VOLT:INP2:VAL -50.0000; * OPC?
:SYST:ERR? -- check for errors --
:CAL:VOLT:STOR yyyymmdd -- enter calibration date --
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Voltage Reference 7-5