Doric Instruments 473 Series Portable Digital Calibrators Calibration Manual - Manual (Page 2)

j. Adjust source output to +27.000 mV.
k. Adjust R9 on Analog Board for an exact display reading of 27.00 mV.
l. Repeat steps 3.1.1g through 3.1.1.k as required until no further adjustment is required
for correct display readings.
m. Switch instrument to low resolution display (.0) and verify display readings of –7.0
mV, 0.0 mV, and 27.0 mV with an input of –7.00 mV, 0.000 mV, and 27.000 mV
respectively.
n. Perform temperature calibration as outlined in 3.1.2.
3.1.2 Temperature Calibration
This procedure required a recirculating ice bath and a Type K thermocouple probe and a
precision millivolt/microvolt source. The probe is constructed as follows: With a
suitable length of type K thermocouple wire and copper hookup wire, form functions
between each thermocouple wire (Hi and Lo) with a length of copper wire. Electrically
isolate these junctions and insert both junctions in a recirculating ice bath. The
calibration setup is shown in Figure 3-2.
a. Set instrument to indicator mode, Type K range, 0.1 resolution,
°
F scale.
b. Observing proper polarity, connect the thermocouple wires from the ice bath to the
instrument T/C input.
c. Observing proper polarity, connect the copper wires from the ice bath to the calibrator
source.
d. Adjust source output to 0.000 mV (short). Allow 15 minutes for stabilization.
e. Adjust R6 on Analog Board for display reading of 32.0
°
F.
f. Adjust source to –4.513 mV.
g. Adjust R28 on Analog board for a display reading of –209.0
°
F.
h. Recheck display with zero input. Adjust R6 as required for a display reading of 32.0
°
F.
i. Adjust source output to +7.848 mV.
j. Adjust R9 on Analog board for a display reading of 379.0
°
F.
k. Repeat steps 3.1.2.2f through 3.1.2.2.j until no further adjustments are required for
correct display readings.
l. Set instrument to indicator mode, mV input
m. Check the display reading with the following inputs: -7.000mV (-7.00 mV display),
0.000 mV (.00 mV display), +27.00 mV display). All readings should be within a
tolerance of + .01. If not the entire calibration procedure must be repeated.
n. Perform mA input calibration as outlined in 3.1.3 next.