Chapter 2  Service
The HP 53181A Calibration Procedures
Assembly-Level Service Guide 2-31
2
The HP 53181A Calibration Procedures
First Determine the Counter Firmware Revision
Press and hold Recall (Utility) key, then cycle POWER key.
REV: n
 is displayed; where “n” represents the numeric firmware revision 
code.
NOTE
After completing the instrument calibration, BE SURE to secure the 
calibration by performing the procedure in the section titled “To Secure 
Against Calibration” on page 2-29 of this chapter.
To Calibrate the Offset for Channel 1
1 To access the Calibration menu, power down, and press and hold 
the Scale & Offset key, then press POWER key.
The first item in the Calibration menu is a message indicating the 
calibration security status: 
CAL SECURE
 or 
CAL UNSECURE
.
The Counter calibration must be unsecured to perform calibration. 
If
CAL UNSECURE
 is displayed, the Counter is already unsecured for 
calibration; go to step 5. However, if 
CAL SECURE
 is displayed then 
perform steps 2 through 4 to unsecure calibration.
2Press Scale & Offset key until 
CODE: 0
 is displayed.
3 Press the appropriate arrow keys to enter the security code 
“
53181
”, for example, if 53181 is the security code by performing 
the following steps:
a. Press   key four times.
The Counter should display 
CODE: 00000
. 
b. Press   key five times.
The Counter should display 
CODE: 50000
.