AD595AD Analog Devices Inc, AD595AD Datasheet - Page 6

• Manufacturer Part Number: AD595AD
• Description: IC THERMOCOUPLE INSTR AMP 14CDIP
• Manufacturer: Analog Devices Inc

Specifications of AD595AD

• Rohs Status: RoHS non-compliant
• Function: Thermocouple Amplifier
• Topology: Ice Point Compensation, Overload Detection
• Sensor Type: External
• Output Type: Voltage
• Output Alarm: Yes
• Output Fan: No
• Voltage - Supply: 5 V ~ ±15 V
• Operating Temperature: -55°C ~ 125°C
• Mounting Type: Through Hole
• Package / Case: 14-CDIP (0.300", 7.62mm)
• Ic Output Type: Voltage
• Sensing Accuracy Range: ± 3°C
• Supply Current: 160µA
• Supply Voltage Range: 5V To ± 15V
• Sensor Case Style: DIP
• No. Of Pins: 14
• Svhc: No SVHC (18-Jun-2010)
• Operating: RoHS Compliant
• Temperature Sensing Range: -55°C To +125°C
• Rohs Compliant: No
• Sensing Temperature: -

AD594/AD595
of R3 should be approximately 280 k . The final connection
diagram is shown in Figure 7. An approximate verification of
the effectiveness of recalibration is to measure the differential
gain to the output. For type E it should be 164.2.
When implementing a similar recalibration procedure for the
AD595 the values for R1, R2, R3 and r will be approximately
650 , 84 k , 93 k and 1.51, respectively. Power consump-
tion will increase by about 50% when using the AD595 with
type E inputs.
Note that during this procedure it is crucial to maintain the
AD594/AD595 at a stable temperature because it is used as the
temperature reference. Contact with fingers or any tools not at
ambient temperature will quickly produce errors. Radiational
heating from a change in lighting or approach of a soldering iron
must also be guarded against.
USING TYPE T THERMOCOUPLES WITH THE AD595
Because of the similarity of thermal EMFs in the 0 C to +50 C
range between type K and type T thermocouples, the AD595
can be directly used with both types of inputs. Within this ambi-
ent temperature range the AD595 should exhibit no more than
an additional 0.2 C output calibration error when used with
type T inputs. The error arises because the ice point compensa-
tor is trimmed to type K characteristics at 25 C. To calculate
the AD595 output values over the recommended –200 C to
+350 C range for type T thermocouples, simply use the ANSI
thermocouple voltages referred to 0 C and the output equation
given on page 2 for the AD595. Because of the relatively large
nonlinearities associated with type T thermocouples the output
will deviate widely from the nominal 10 mV/ C. However, cold
junction compensation over the rated 0 C to +50 C ambient
will remain accurate.
STABILITY OVER TEMPERATURE
Each AD594/AD595 is tested for error over temperature with
the measuring thermocouple at 0 C. The combined effects of
cold junction compensation error, amplifier offset drift and gain
error determine the stability of the AD594/AD595 output over
the rated ambient temperature range. Figure 8 shows an AD594/
AD595 drift error envelope. The slope of this figure has units
of C/ C.
+0.6 C
Figure 8. Drift Error vs. Temperature
–0.6 C
Figure 7. Type E Recalibration
0
14
1
9
8
TEMPERATURE OF AD594C/AD595C
FB
+IN
–IN
VO
AD594/
AD595
R3
25 C
COM
+C
–C
+T
–T
4
3
2
6
5
R1
R2
50 C
–6–
THERMAL ENVIRONMENT EFFECTS
The inherent low power dissipation of the AD594/AD595 and
the low thermal resistance of the package make self-heating
errors almost negligible. For example, in still air the chip to am-
bient thermal resistance is about 80 C/watt (for the D package).
At the nominal dissipation of 800 W the self-heating in free air
is less than 0.065 C. Submerged in fluorinert liquid (unstirred)
the thermal resistance is about 40 C/watt, resulting in a self-
heating error of about 0.032 C.
SETPOINT CONTROLLER
The AD594/AD595 can readily be connected as a setpoint
controller as shown in Figure 9.
The thermocouple is used to sense the unknown temperature
and provide a thermal EMF to the input of the AD594/AD595.
The signal is cold junction compensated, amplified to 10 mV/ C
and compared to an external setpoint voltage applied by the
user to the feedback at Pin 8. Table I lists the correspondence
between setpoint voltage and temperature, accounting for the
nonlinearity of the measurement thermocouple. If the setpoint
temperature range is within the operating range (–55 C to
+125 C) of the AD594/AD595, the chip can be used as the
transducer for the circuit by shorting the inputs together and
utilizing the nominal calibration of 10 mV/ C. This is the centi-
grade thermometer configuration as shown in Figure 13.
In operation if the setpoint voltage is above the voltage corre-
sponding to the temperature being measured the output swings
low to approximately zero volts. Conversely, when the tempera-
ture rises above the setpoint voltage the output switches to
the positive limit of about 4 volts with a +5 V supply. Figure
9 shows the setpoint comparator configuration complete with a
heater element driver circuit being controlled by the AD594/
AD595 toggled output. Hysteresis can be introduced by inject-
ing a current into the positive input of the feedback amplifier
when the output is toggled high. With an AD594 about 200 nA
into the +T terminal provides 1 C of hysteresis. When using a
single 5 V supply with an AD594, a 20 M resistor from V
+T will supply the 200 nA of current when the output is forced
high (about 4 V). To widen the hysteresis band decrease the
resistance connected from VO to +T.
TEMPERATURE
CONTROLLED
REGION
HEATER
IRON
(CHROMEL)
CONSTANTAN
(ALUMEL)
Figure 9. Setpoint Controller
HEATER
DRIVER
14
1
AD594/
AD595
G
13
2
TEMPERATURE
COMPARATOR OUT
12
3
OVERLOAD
DETECT
+5V
G
11
4
+A
COMMON
10
5
+TC
9
6
COMP.
POINT
LOW = > T < SETPOINT
HIGH = > T > SETPOINT
ICE
8
7
–TC
SETPOINT
VOLTAGE
INPUT
20M
(OPTIONAL)
FOR
HYSTERESIS
REV. C
O
to