Fluke 45 - 5-18. Calibration-Related Components

45
Service Manual
5-20
and a displayed ’Error’ at the front panel and a device dependent error over the computer
interface. These indications occur if the input varies from what the meter expects to see
by more than ±15%. After one second, the meter reverts to normal operation in
calibration mode.
Before suspecting a fault with the Fluke 45, verify that the calibration is being conducted
properly.
• Check the connections between the source and the meter. Are all the connections in
place.
• Check the output of the calibration source. Does it equal the value called for by this
calibration step?
• Check the calibration source. Is it in operate mode? Has it reverted to standby?
If the calibration setup is correct, a faulty component within the Fluke 45 may be causing
the failure. Each measurement function depends on a combination of components in and
around the Analog Measurement Processor (A1U1). Basic dc measurements depend on
the zener reference (A1VR1), reference divider network (A1Z3), and integrate resistors
(A1Z3). Resistance measurements and dc measurements above three volts additionally
depend on the resistors in the dc divider network (A1Z1). AC measurements depend on
the ac divider network (A1Z2), ac buffer (A1AR1), and rms converter (A1A1), as well
as the basic dc measurement components.
Note
The Fluke 45 utilizes three measurement rates: slow, medium, and fast.
Two sets of measurement ranges are used: one for the medium and fast
rates and one for the slow rate. Whenever the meter is powered-up or put
in calibration mode, the medium rate is selected. During calibration, the
slow rate is selected automatically as required by the calibration step.
5-18. Calibration-Related Components
Measurement function calibration depends on various combinations of components in
and around the Analog Measurement Processor. The major components are:
• Rms Converter A1A1
• AC Buffer A1AR1
• Shunt Resistors A1R2, A1R3
• Zener Reference A1VR1
• Divider Network (DC/Ohms) A1Z1
• Integrate Resistors, Reference Divider A1Z3
• AC Divider Network A1Z2
• Rms Converter Network A1Z4
Calibration of the Fluke 45 utilizes a building block approach; individual components
are calibrated separately and the appropriate calibration building blocks are assembled
later for correction of any particular measurement function, range, and rate. Calibration
steps are grouped by function, with dc volts being first.
Therefore, the calibration constants are partitioned to allow for some independence in
the correction of the various measurement functions. For example, if the zener reference
and divider needed replacing, it would be necessary to recalibrate dc volts only; ac volts
would not be affected. Table 5-6 identifies components that are unique to each