Racal Instruments 2251A Operator's Manual page 63

4.1.5 Diagnostic Special Functions
4.1.5.0.1 It is recommended that the following Special Functions are enabled in turn in the
check mode and the results noted before commencing the Performance Verification
Procedures for the counter. Successful completion of this procedure demonstrates
that the 2251A measurement circuitry is functioning correctly.
S70 Frequency Measurement Check. Expected result: CK+10.000000000e+06
S72 START TEC Short Calibration.
S73 START TEC Long Calibration.
S74 STOP TEC Short Calibration.
S75 STOP TEC Long Calibration.
S77 Input A relays check
S78 Input B relays check.
The expected results for S73 and S75 are 800 ± 220. The expected results for S72
and S74 are (S73 result) / 2, tolerance +20, -40 and (S75 result) / 2, tolerance + 20,
-40, respectively.
For S77 and S78 tests, it is necessary to input a 10MHz square wave signal with
amplitude of a positive peak between +.8V and +1.0V, and a negative peak between
-.2V and -.4V 6. A successful completion of the relays results in an output of
CK+0000000000.0E000. Error Codes are described in Section 3.4.
4.1.5.0.2 Check mode Special Functions S72 - S78 may be exited by selecting S70 (Basic
Check function) or any other measurement mode.
4.1.5.3 Special Functions S77 and S78 require a time delay between initiation of check and
reading of data. S77 requires a 9 second delay and S78 requires a 1 second delay.
4-2
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