LM363 Datasheet, PDF (16/22 Pages) National Semiconductor (TI) – LM363 Precision Instrumentation Amplifier

Typical Applications (Continued)
Curvature Corrected Platinum RTD Thermometer
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70k and 2k should track to 5 ppm C
Less than 5 ppm C drift
Less than 100 ppm C drift
These resistors should track to 20 ppm C
Equivalent circuit showing lead resistance
This thermometer is capable of 0 01 C accuracy over b50 C to
a150 C A unique trim arrangement eliminates cumbersome trim inter-
actions so that zero gain and nonlinearity correction can be trimmed in
one oven trip Extra op amps provide full Kelvin sensing on the sensor
without adding drift and offset terms found in other designs A2 is con-
figured as a Howland current pump biasing the sensor with a fixed
current
Resistors R2 R3 R4 and R5 from a bridge driven into balance by A1 In
balance both inputs of A1 are at the same voltage Since R6eR7 A1
draws equal currents from both legs of the bridge Any loading of the
R4 R5 leg by the sensor would unbalance the bridge therefore both
bridge taps are given to the sensor open circuit voltage and no current
is drawn
Precision Temperature Controller
Ultronix 105A wirewound
ThermistoreYellow Springs 44032
Setpoint stabilitye2 5X10^b4 C Hr
16
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