Doric Instruments 475 Series Portable Digital Calibrators Calibration Manual - Manual (Page 2)

3.1.1 Disassembly
a. Remove battery from instrument (refer to 2.4.1).
b. Remove bottom case half from printed circuit board assemblies by extracting
three screws from case bottom and one screw holding wrist strap lug.
c. Remove top case half from printed circuit board assemblies by extracting screw
on clad side of Analog board between output controls.
d. Re-connect battery to connector.
3.2.1 RTD/Ohm Calibration
a. Set RTD switch to 2-/4-wire position.
b. Set mA switch to “A” position.
c. Connect precision resistance decade box to instrument input using supplied 4-wire
leadset: connect V+ and I+ jacks to one terminal of decade box; connect V- and
I- jacks to other terminal of decade box. Use supplied mini-banana adapters as
required to connect decade box.
d. Turn instrument on and wait five minutes for stabilization.
e. Select: indicate mode, Pt392 range,
°
F readout, .1 resolution
f. Set decade box to 100.00 ohms
g. Adjust R24 for a display reading of 32.0
°
F.
h. Set decade box to 176.90 ohms
i. Adjust R27 for a display reading of 390.0
°
F.
j. Set decade box to 59.00 ohms
k. Adjust R33 for a display reading of –150.0
°
F.
l. Repeat steps 3.1.2.e through 3.1.2.k until no further adjustments are required
m. Select Pt385 range.
n. Set decade box to 175.43 ohms
o. Adjust R17 for a display reading of 390.0
°
F.
p. Select: Cu10 range,
°
C readout.
q. Set decade box to 9.04 ohms.
r. Adjust R7 for a display reading of 0
°
C.
s. Select
°
F readout.
t. Adjust R5 for a display reading of 32
°
F.
u. Select
°
C readout.
v. Set decade box to 16.780 ohms.
w. Adjust R19 for a display reading of 200
°
C.
x. Select
°
F readout; display should read 392
°
F.
y. Repeat steps 3.1.2.p through 3.1.2.x until no further adjustments are required for
correct display readings.
z. Select ohms range.
aa. Select decade box to 0.00 ohms.
bb. Adjust R10 for display readings of 00 and 0.0 for 1 ohm and .1 ohm ranges
respectively.
cc. Set decade box to 1000.0 ohms.
dd. Adjust R52 for a display reading of 1000 ohms.
ee. Set decade box to 390.0 ohms.
ff. Select .1 ohm resolution.