AD8497 AD [Analog Devices], AD8497 Datasheet - Page 15

• Manufacturer Part Number: AD8497
• Description: Precision Thermocouple Amplifiers with Cold Junction Compensation
• Manufacturer: AD [Analog Devices]

SETPOINT CONTROLLER
The AD849x can be used as a temperature setpoint controller,
with a thermocouple input from a remote location or with the
AD849x itself being used as a temperature sensor. When the
measured temperature is below the setpoint temperature, the
output voltage goes to −V
above the setpoint temperature, the output voltage goes to +V
For best accuracy and CMRR performance, the setpoint voltage
should be created with a low impedance source. If the setpoint
voltage is generated with a voltage divider, a buffer is
recommended.
Hysteresis can be added to the setpoint controller by using a
resistor divider from the output to the reference pin, as shown
in Figure 36. The hysteresis in °C is
A resistor equivalent to the output resistance of the divider should
be connected to the sense pin to ensure good CMRR.
1MΩ
1MΩ
THERMO-
THERMO-
COUPLE
COUPLE
T
HYST

V
Figure 36. Adding 10 Degrees of Hysteresis
S

+IN
–IN
+IN
–IN
5
R1
mV/
Figure 35. Setpoint Controller
8
1
8
1
1kΩ
/(
R1
R1

COLD JUNCTION
COMPENSATION
REF
COLD JUNCTION
COMPENSATION
REF
C
IN-AMP
IN-AMP

S
. When the measured temperature is
R2
2
2
)
AD849x
AD849x
100kΩ
3
3
R2
–V
–V
5V
5V
7
7
S
S
+V
+V
S
S
6
5
6
5
SENSE
OUT
SENSE
OUT
R1
1kΩ
SETPOINT
VOLTAGE
SETPOINT
VOLTAGE
Rev. 0 | Page 15 of 16
S
.
MEASURING NEGATIVE TEMPERATURES
The AD849x can measure negative temperatures on dual
supplies and on a single supply. When operating on dual
supplies with the reference pin grounded, a negative output
voltage indicates a negative temperature at the thermocouple
measurement junction.
When operating the AD849x on a single supply, level-shift
the output by applying a positive voltage (less than +V
the reference pin. An output voltage less than V
a negative temperature at the thermocouple measurement
junction.
REFERENCE PIN ALLOWS OFFSET ADJUSTMENT
The reference pin can be used to level-shift the AD849x output
voltage. This is useful for measuring negative temperatures on a
single supply and to match the AD849x output voltage range to
the input voltage range of the subsequent electronics in the
signal chain.
The reference pin can also be used to offset any initial calibra-
tion errors. Apply a small reference voltage proportional to the
error to nullify the effect of the calibration error on the output.
V
OUT
= ( T
AD8494/AD8495/AD8496/AD8497
MJ
× 5 mV/°C) + V
REF
REF
indicates
S
) on