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TMP17GS View Datasheet(PDF) - Analog Devices

Part NameDescriptionManufacturer
TMP17GS Low Cost, Current Output Temperature Transducer ADI
Analog Devices ADI
TMP17GS Datasheet PDF : 8 Pages
1 2 3 4 5 6 7 8
TMP17
+5V
TMP17
333.3
(0.1%)
VTAVG (1mV/K)
+15V
TMP17
TMP17
TMP17
10k
(0.1%)
VTAVG (10mV/K)
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.
+V
TMP17
R1
TMP17 50k
5M
10k
10k
OP196
VOUT = (T1 – T2) x
(10mV/oC)
–V
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) temperature
measurements can be made with higher resolution. If the
magnitude of Vϩ and VϪ 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.
MEASURING
JUNCTION
+7.5V
2.5V
REF43
10k
Cu
1k
TMP17
REFERENCE
Cu JUNCTION
100k
THERMOCOUPLE
TYPE
J
K
T
E
S
R
APPROX.
R VALUE
52
41
41
61
6
6
OP193
VOUT
RG2
(1k)
RG1
R
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 RG1 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 ksystems.
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.
REF01E
TMP17
35.7k
10mV/ C RT
5k
17 C 4mA
33 C 20µA
1mA/ C
+20V
OP97
C
10k12.7k
5k500
10
VT
–20V
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.
+5V
REF43
2.5V
ROFFSET
R
RCAL
ROFFSET/RGAIN
RGAIN
OP196
ROFFSET
C 9.1k
F 9.8k
RGAIN
100k
180k
VOUT = 100mV/( C OR F)
TMP17
V–
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.
–6–
REV. 0
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