LM185-1.2/LM285-1.2/LM385-1.2
Typical Applications
METER THERMOMETERS
(Continued)
0˚C−100˚C Thermometer
Micropower Thermocouple Cold Junction
Compensator
00551828
Calibration
1. Short LM385-1.2, adjust R3 for I
OUT
= temp at 1µA/˚K
2. Remove short, adjust R2 for correct reading in centigrade
†
I
Q
at 1.3V.500µA
00551831
I
Q
at 1.6V.2.4mA
Adjustment Procedure
1. Adjust TC ADJ pot until voltage across R1 equals Kelvin temperature
multiplied by the thermocouple Seebeck coefficient.
Lower Power Thermometer
2. Adjust zero ADJ pot until voltage across R2 equals the thermocouple
Seebeck coefficient multiplied by 273.2.
Thermocouple
Type
Seebeck
R1 R2
Voltage
Across
R1
@
25˚C
Voltage
Across
R2
(mV)
14.32
11.78
11.17
1.766
Coefficient (Ω) (Ω)
(µV/˚C)
(mV)
J
T
00551829
52.3
42.8
40.8
6.4
523
1.24k
432 1k
412
953Ω
63.4
150Ω
15.60
12.77
12.17
1.908
*2N3638 or 2N2907 select for inverse H
FE
.
5
†
Select for operation at 1.3V
‡
I
Q
.
600µA to 900µA
K
S
0˚F−50˚F Thermometer
00551830
Calibration
1. Short LM385-1.2, adjust R3 for I
OUT
= temp at 1.8µA/˚K
2. Remove short, adjust R2 for correct reading in ˚F
Typical supply current 50µA
7
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