Curvature Corrected Platinum RTD Thermometer

TLH5609 – 23

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

a

150 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

draws equal currents from both legs of the bridge Any loading of the

R4R5 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

TLH5609 – 24

Ultronix 105A wirewound

44032

16