Fluke 540B - Protection Disable Check (Model A54-2); Transfer Calibration Check

540B
ceed as follows:
a. Remove Q304 from the 540B-401 circuit board
(Search and Protection Amplifier PCB}.
b. POWER switch to OFF.
c. With an ohmmeter (Simpson 260 or equivalent) check
the resistance between the mounting screw of T2 on
printed circuit board 840A-401 and 540B chassis
.ground. Place the probe or positive connection of
the ohmmeter to ground .
d. The resistance must be 40k or higher.
e. Replace Q304.
4-30. GALVANOMETER INPUT ISOLATION
4-31. The purpose of this test is to assure the isolation
of
the galvanometer input circuit from galvanometer
ground. It is necessary to use an instrument capable of
measuring 100 megohms. The following procedure is
intended for use with a FLUKE differential voltmeter,
such as the Model 885 suggested in Figure 4- 1. Re-
move the HIGH FREQ CONVERTER p lug and proce ed
as follows:
a. POWER switch to OFF.
b. SENSITIVITY switch to LOW.
c. GALV switch to OPEN.
d. Connect the 885
differential voltmeter to either end
of R16 and one of the T2 mounting screws (see
Figure 4-4).
e. Dial the voltmeter to 10 volts.
f. Place the NULL switch in the . 001 position.
g. The Model 885 meter deflectio n must be less than
full scale.
h. Disconnect the Model 885 and replace the HIGH
FREQ CONVERTER plug.
4 -32. PROTECTION DISABLE CHECK (Model A54-2)
4-33. During de or low frequency (up to 10kHz) ac
transfer measurements, the PROTECTION DISABLE
switch can be actuated to verify correct operation. When
actuated, a resulting GALVANOMETER meter deflection
greater than one minor division indicates incorrect oper-
ation. The diode protection bridge should be investi-
gated f or component failu re should this occur. At fre-
quencie s higher than 10 kHz a meter deflection greater
than one minor divi.sion will be noted. This is normal
for the instrument.
4-34. TRANSFER CALIBRATION CHECK
4- 35. The following procedure is intended to check,
rather than calibrate, the transfe r ranges of the Model
4-6
540B. It is essential that the person checking the cali-
bration be thoroughly familiar with the use of the Model
540B and the
system being used as a calibration standard
before attempting these procedures. It is suggested that
every measurement in this procedure be accomplished
at least four times or until repeatability is attained.
The de reference voltage should be checked immediately
after any measurement to assure its stability. Should
it be impossible to a tta in a good degree of repeat ability
in any test, the result s of th at test are not reliable and
should be disregarded until repeatability is attained.
a. Connect the equipment as shown in F i gure 4-5
observing the precautions mentioned in Sect ion 2-9.
Note!
When connecting the transfer standards as
shown in Figure 4-5, it is mand atory that
the leads be kept as short as possible. It is
also necessary that all ac leads have losses
equal to the losses in the comparable de
leads. Ten milliohms of lead loss differ-
ence represents a . 01% error in the transfer
readings on the 0. 5 volt range.
b. Prepare a test record similar to the one shown in
Figure 4- 5.
c. Take reversal error readings on both transfer
standards as explained in Section 2-15 and record
the results on the test record.
Note!
In order to conform with National Bureau of
Standards notations, all deflections of the
Galvanometer to the left (less input) are
assigned + and all deflection to the right
(more input) are assigned - notation.
d.
The reversal error measured shouid be divided by
2 and entered as the Corr ected Zero as shown in the
example. This corrected zero will be the zero
setting for all de inputs for the remainder of the
tests.
e. In the column TEST REPORT CORRECTIONS enter
the correction figures given in the Test Report of
the instrument being used as the standard instru-
ment.
f. Apply 0. 5 volts of de to the coaxial "T" connector
and apply 0. 5 volts rms ac of the desired check
frequency to the adjacent coaxial "T" connector.
g. With both Transfer Standards in the DC TRAN SFER
MODE of opera tion proceed to null the galvano-
meters using the lindecks or other referenc e adjust
controls on succeedingly more sensitive positions
of the galvanometers until both galvanometers are
nulled at the Corrected Zero points as computed on
the test record.
h. Deflection sensitivity should be computed as per
Section 2-13 so that all remaining readings may be
properly recorded on the test record.
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