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197A calibration revisions

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jvincent
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Joined: June 10th, 2010, 11:20 am
Country: United States

197A calibration revisions

Post by jvincent » September 8th, 2010, 6:09 am

I have two 197As. I need to calibrate them.
One has a cal switch in the rear panel the other does not.
What is the difference?

Dale C
Keithley Applications
Keithley Applications
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Joined: June 10th, 2010, 6:22 am
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Re: 197A calibration revisions

Post by Dale C » September 8th, 2010, 6:21 am

Depending on the firmware revision, there are three methods to put these
instruments (197A, 175A and 485) in the CAL ENABLE mode. See details below.

Firmware A revision : Has an internal cal enable switch.
Firmware B revision: NO internal cal enable switch, performed digitally through sequence during power up. (see procedure below)
Firmware C revision : Has external cal enable switch on rear. Procedure for CAL ENABLE for Revision B firmware:

In Service Manual, delete paragraph 5.6.3 Calibration Jumper on page 5-4 and Figure 5-2 on page 5-5 and replace with the following:

5.6.3 Calibration Storage Enable

The Model must be in the calibration storage enable mode in order to realize storage of calibrations constants into the NVRAM. If the instrument is not placed in this mode, subsequent calibration will be lost when the instrument is turned off. Perform the following steps to place the unit in storage enable mode:

Turn unit off While holding in the STO/CLR button, turn the instrument on using the ON/OFF switch. When the "CAL" message is displayed, release the STO/CLR button. This instrument will return to normal display mode, and the storing of calibration constants is now enabled.

Allow 1 hour warm up before proceeding with instrument calibration. Press in the REL and dB pushbuttons simultaneously until the message "CAL" is displayed again. Release the buttons. The unit is now ready to be calibrated as indicated by the "C" annunciator on the display.

Note: Step 2 and 3 put the instrument in the CAL ENABLE mode, while step 5 puts the instrument in the CAL mode.

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