26
27
12.0 CALIBRATION SERVICE
Recalibration service can be provided at a nominal cost, if desired. Special
thermal calibration traceable to NIST is available. Standard temperature
points are: 0°C, 94°C, and 250°C. Custom points are available upon request.
13.0 700M THERMISTOR .01°C/F RESOLUTION HEAT PROBER
13.1 General Discussion
The Wahl Thermistor unit measures temperature over a range of -1.00°C to
60.99°C (30.20°F to 141.78°F) with .01°C resolution. The sensing element in
the probes is a highly stable thermistor, with .1°C interchangeability, the out-
put being processed and linearized before display. The accuracy of the meter
is .02°C. With probe installed, the accuracy is .04°C.
The signal conditioning circuitry is completely chopper stabilized and associ-
ated resistive components have a very low temperature coefficient. This com-
bination yields essentially drift free operation.
The linearization of the Thermistor sensor is accomplished in two steps for
best utilization of the available analog-to-digital converter range. A resistive
network accomplishes a portion of the linearization while a look-up” table in
the microprocessor completes the balance.
All operations of the instrument are controlled by the microprocessor includ-
ing the drive for the display and peak reading computation and retention.
Another important feature of the instrument is the use of dual power regula-
tors and dual grounding systems to provide the ultimate in isolation between
sensitive signal conditioning circuits and the high level digital processing and
display circuits.
The power source of the 700M is the same as the 392M, which is a recharge-
able nickel-cadmium battery pack composed of five AA size cells with a com-
bined voltage of 6.0 volts and capacity rating of .65 amp-hours. The unit is
supplied with a recharger which can be plugged in at any time to maintain
the charge of the battery pack. Low battery condition is displayed as “L” in
the left-hand side of the display. The 700M is available only with LED display.
Should the temperature being measured extend beyond the limits of the
instrument, or in the event the probe is removed from the unit or becomes
defective and opens, an indication of -OL- will be displayed on the LED dis-
play. Correcting the over/under range condition or inserting a functioning
probe will again bring the instrument to a proper indicating condition.
T
OLERANCE
(P
ROBE
I
NTERCHANGEABILITY
)
Temp °C
-250
-220
-200
-100
0
100
200
300
400
500
Tolerance
±°C
5.8
1.8
1.2
0.7
0.3
0.5
1.1
1.7
2.3
3.0
±:
1.0
0.7
0.5
0.3
0.1
0.2
0.4
0.6
0.8
1.0
T
OLERANCE
(P
ROBE
I
NTERCHANGEABILITY
)
°F
0
-20
-40
-60
-80
-100
-120
-140
-160
-180
-200
0
93.03
88.65
84.26
79.85
75.42
70.98
66.52
64.04
57.54
°F
0
20
40
60
80
100
120
140
160
180
200
0
93.03
97.39 101.74 106.07 110.38 114.68 118.97 123.24 127.50 131.74 135.97
200
135.97 140.18 144.38 148.57 152.74 156.90 161.04 165.17 169.28 173.28 177.47
400
177.47 181.54 185.60 189.64 193.67 197.69 201.69 205.68 209.65 213.61 217.55
600
217.55 221.49 225.40 229.31 233.20 237.07 240.93 244.78 248.61 252.43 265.23
800
256.23 260.02 263.80 267.56 271.31 275.04 278.76 282.46 286.15 289.83 293.49
T
OLERANCE
(P
ROBE
I
NTERCHANGEABILITY
)
Temp
°C
-420 -400 -350 -300 -200 -100
0
32
100 200 300 400 500 600 700 800 900
Tolerance
±°C
10.4
8.3
3.3
1.9
1.5
1.1
0.7 0.6
0.7
0.9
1.5
2.0
2.7
3.3
3.9
4.5
5.4
±:
1.0
0.9
0.7
0.5
0.4
0.3
0.2 0.1
0.2
0.2
0.3
0.4
0.6
0.7
0.8
0.9
1.0