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TMP17 Datasheet(PDF) 6 Page - Analog Devices

Part No. TMP17
Description  Low Cost, Current Output Temperature Transducer
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TMP17 Datasheet(HTML) 6 Page - Analog Devices

   
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TMP17
REV. 0
–6–
TMP17
VT
AVG
(1mV/K)
TMP17
+5V
333.3
(0.1%)
VT
AVG
(10mV/K)
10k
(0.1%)
+15V
TMP17
TMP17
Figure 13. Average and Minimum Temperature
Connections
The circuit of Figure 14 demonstrates a method in which a
voltage output can be derived in a differential temperature
measurement.
R1
50k
10k
OP196
VOUT = (T1 – T2) x
(10mV/oC)
10k
5M
–V
+V
TMP17
TMP17
Figure 14. Differential Measurements
R1 can be used to trim out the inherent offset between the two
devices. By increasing the gain resistor (10 k
Ω) temperature
measurements can be made with higher resolution. If the
magnitude of V
and V
is not the same, the difference in
power consumption between the two devices can cause a
differential self-heating error.
Cold junction compensation (CJC) used in thermocouple signal
conditioning can be implemented using a TMP17 in the circuit
configuration of Figure 15. Expensive simulated ice baths or
hard to trim, inaccurate bridge circuits are no longer required.
OP193
REFERENCE
JUNCTION
100k
10k
VOUT
+7.5V
MEASURING
JUNCTION
1k
TMP17
R
THERMOCOUPLE
TYPE
APPROX.
R VALUE
J
K
T
E
S
R
52
41
41
61
6
6
2.5V
REF43
RG1
RG2
(1k
Ω)
Cu
Cu
Figure 15. Thermocouple Cold Junction Compensation
The circuit shown can be optimized for any ambient tempera-
ture range or thermocouple type by simply selecting the correct
value for the scaling resistor – R. The TMP17 output (1
µA/K)
times R should approximate the line best fit to the thermocouple
curve (slope in V/
°C) over the most likely ambient temperature
range. Additionally, the output sensitivity can be chosen by
selecting the resistors R
G1 and RG2 for the desired noninverting
gain. The offset adjustment shown simply references the
TMP17 to
°C. Note that the TC’s of the reference and the
resistors are the primary contributors to error. Temperature
rejection of 40 to 1 can be easily achieved using the above
technique.
Although the TMP17 offers a noise immune current output, it
is not compatible with process control/industrial automation
current loop standards. Figure 16 is an example of a tempera-
ture to 4–20 mA transmitter for use with 40 V, 1 k
Ω systems.
In this circuit the 1
µA/K output of the TMP17 is amplified to
1 mA/
°C and offset so that 4 mA is equivalent to 17°C and
20 mA is equivalent to 33
°C. Rt is trimmed for proper reading
at an intermediate reference temperature. With a suitable choice
of resistors, any temperature range within the operating limits of
the TMP17 may be chosen.
TMP17
REF01E
35.7k
10mV/ C
10k
12.7k
5k
500
+20V
–20V
VT
10
C
RT
5k
1mA/ C
OP97
17 C
≈ 4mA
33 C
≈ 20µA
Figure 16. Temperature to 4–20 mA Current Transmitter
Reading temperature with a TMP17 in a microprocessor based
system can be implemented with the circuit shown in Figure 17.
R
ROFFSET/RGAIN
OP196
VOUT = 100mV/( C OR F)
+5V
REF43
V–
C
F
≈ 9.1kΩ
≈ 9.8kΩ
100k
180k
RGAIN
ROFFSET
TMP17
RCAL
2.5V
RGAIN
ROFFSET
Figure 17. Temperature to Digital Output
By using a differential input A/D converter and choosing the
current to voltage conversion resistor correctly, any range of
temperatures (up to the 145
°C span the TMP17 is rated for)
centered at any point can be measured using a minimal number
of components. In this configuration the system will resolve up
to 1
°C.


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