Service Information
4-11
use a lower resistance range.) Let the Model 2001 warm
up for one hour.
2. Set another Model 2001 to the 200mV DC range. Insert
a 2-terminal low thermal shorting bar into the voltage in-
puts. Zero the Model 2001 after one hour, and remove
the shorting bar.
3. Set up the test equipment as shown in Figure 4-7. Re-
move the cover of the Model 2001 as explained in para-
graph 4.7.2.
4. Remove the card top shield and cable clamp. Insert the
card into the Model 2001, and protect it from air drafts.
5. Coat the probe with a thermally conductive compound,
and insert it into the 0.110-inch hole marked “CAL” on
the PC board.
6. Take a reading of the probe resistance when it stabilizes.
7. Using the lookup tables for the CSP A207A probe, find
the Celsius temperature that corresponds to the above
probe resistance. This value is the temperature of the
isothermal block as measured by the probe.
8. The following equation calculates the equivalent refer-
ence junction output voltage (V
REF
):
V
REF
= (T
J
+ 273.15)
×
0.0002
9. Close Channel 1 on the Model 2001-TCSCAN card, and
read the output voltage; it should equal the V
REF
voltage
just calculated. Adjust trimmer R151 until the equiva-
lent temperature equals:
probe temp.
±
0.05
°
C
10. Check the probe resistance again, and find the corre-
sponding temperature with the lookup tables. If the new
value differs by more than 0.01
°
C from the temperature
found in step 7, repeat steps 8 and 9.
4.4.2 Calibration with thermocouple wire
This procedure compensates for errors of the reference junc-
tion circuitry and establishes a compensation factor for the
offset of the particular piece of thermocouple wire. Because
of an inherent error source, (the thermocouple wire used in
measuring the ice-point), absolute calibration accuracy can-
not be guaranteed.
Assuming the homogeneity of the thermocouple wire spool,
errors due to thermocouple offset voltages will be signifi-
cantly reduced for the entire system. For subsequent applica-
tions of this particular Model 2001-TCSCAN card, the same
spool of wire should be used on the same channel; otherwise
the Model 2001-TCSCAN should be recalibrated. This ex-
ample uses channel 2. Change connections and setup appro-
priately for other channels.
This procedure assumes bench reset conditions on the Model
2001.
1. On the Model 2001-TCSCAN, connect the thermocou-
ple positive lead to Channel 2 HI and the negative lead
(red insulation) to Channel 2 LO. Connect copper wires
to the HI and LO terminals of OUT A. Remove the cable
clamp, and insert a non-metallic screwdriver to adjust
trimmer R151. See Figure 4-8.
2. Insert the Model 2001-TCSCAN into a Model 2001.
Connect the output wires to the INPUT HI and LO ter-
minals of the Model 2001.
3. Turn on the instrument, and allow it to warm up for at
least one hour.
4. Fill a Dewer flask or Thermos half full with pea-sized
ice made from distilled water. Fill up the flask with dis-
tilled water. Stir the contents.
5. Place a twisted or welded thermocouple junction into
the volume of the flask occupied by ice. Cover the flask,
and stir contents occasionally. Allow 20 minutes for
temperature stabilization. Add more ice as necessary.
6. On the Model 2001, select the TEMP function and con-
figure it as follows:
• Select a thermocouple temperature sensor, and
choose the appropriate type.
• Configure reference junction #1 (JCN1) with the
temperature coefficient (+00.20mV/
°C) and offset
voltage (+54.63mV @ 0°C) for the Model 2001-
TCSCAN.
• Select temperature units of DEG-F (to yield better
resolution than DEG-C).
7. From the CONFIG-CHAN menu of the Model 2001, se-
lect internal inputs, the JN1 function for Channel 1, and
the TMP function for Channel 2. (Set all other channels
to ---.)
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