HYDRA

Service Manual

5-20. Calibration Failures

5-21. Introduction

Calibration of Hydra through the computer interface is described in Section 4 of this manual. Generally, a calibration failure is indicated by a Device Dependent Error and a "!>" prompt after a CAL_STEP? command if the RS-232 interface is being used. If the IEEE-488 interface is being used, the Device Dependent Error may be detected by reading the Event Status Register (see the Hydra User Manual). These indications occur if the analog input varies from what the instrument expects to see by more than ±5% or ±15%, depending on the calibration step.

Before suspecting a fault with Hydra, verify that the calibration is being conducted properly.

∙Check the connections between the source and the instrument. Are allthe connections in place?

∙Check the output of the calibration source. Does it equal the valuecalled for by this calibration step?

∙Check the calibration source. Is it in operate mode? Has it revertedto standby?

If a calibration step has failed, Hydra remains on that step so that the output from the calibration source may be corrected or the calibration reference value (CAL_REF) being used by Hydra may be changed if it was improperly entered. The calibration step may be repeated by sending the CAL_STEP? command to Hydra again.

Calibration of Hydra utilizes a simple "calibration by function" approach. If you suspect calibration errors, but the instrument does not exhibit the symptoms mentioned above, verify that you are observing the following calibration rules:

∙Independent calibration of any function results in the storage ofcalibration constants for that function only.

∙Once calibration is begun, all steps for that function must becompleted before the calibration constants are stored. If all stepsare not completed and the procedure is terminated, no constants forthat function are stored; only calibration constants for previouslycompleted functions are stored.

5-22. Calibration-Related Components

If the calibration setup is correct, a faulty component within Hydra may be causing the failure. Each measurement function depends on a combination of components in and around the Analog Measurement Processor (A3U8).

RMS Converter

A3U6

AC Buffer

A3U7

Zener Reference

A3VR1

Divider Network (DC/Ohms)

A3Z4

Integrate Resistors, Reference Divider

A3Z2

AC Divider Network

A3Z3

RMS Converter Network

A3Z1

Basic dc measurements depend on the zener reference (A3VR1), reference divider network (A3Z2), and integrate resistors (A3Z2). Resistance measurements and dc measurements above three volts additionally depend on the resistors in the dc divider network (A3Z4). AC measurements depend on the ac divider network (A3Z3), ac buffer (A3U7), and RMS converter (A3U6), as well as the basic dc measurement components.

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Fluke 2635A, 2625A service manual Calibration Failures, Introduction, Calibration-Related Components
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2635A, 2625A specifications

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