Model 231, 231P, and 234 Temperature Transmitters

Model 231, 231P, and 234 Temperature Transmitters

The 230 Series transmitters are discontinued. Please consider the 240 Series as a replacement.

Model 231, 231P, and 234 Temperature Transmitter Features

  • Sensor input fully isolated from power supply potential
  • Different models support various sensor types
  • 4-lead differential measurement
  • Output range of 4 mA to 20 mA or 0 mA to 20 mA (0 V to 10 V)
  • Available rack-mount case holds up to 12 units 

Model 231 Features

  • Operates from 1.4 K to 500 K with appropriate diode

Model 231P Features

  • Operates from 1.4 K to 800 K with appropriate NTC RTD

Model 234 Features

  • Operates from 100 mK to 420 K with appropriate NTC RTD
  • Includes serial interface

Model 234D Features

  • Operates from 100 mK to 420 K with appropriate NTC RTD
  • Includes serial interface
  • 6-digit LED display
Model 231

The Model 231 operates with either silicon diode or gallium-aluminum-arsenide (GaAlAs) diode sensors.

Excited with a 10 µA current source from the Model 231, the sensors produce a voltage that depends on temperature. A microcontroller reads the voltage through an A/D converter and translates it into temperature using a temperature response curve. The Model 231 includes two standard curves for DT-470 and DT-670 diode sensors. It also supports a single CalCurve™ option for calibrated sensors (TG-120 diodes require a CalCurve™).

Model 231P

The Model 231P uses a PT-100 Series platinum sensor. The Model 231P excites the sensor with a 500 µA current to produce a measurable signal. Either the standard platinum curve (IEC 751) or a CalCurve™ is used for temperature conversion.

Model 234

The Model 234 operates with Cernox®, carbon-glass, germanium, or other negative temperature coefficient (NTC) resistance temperature sensors. The Model 234 excites the sensor with a constant voltage of 10 mV or less to minimize the effects of sensor self-heating at low temperatures.

The Model 234 employs an analog control circuit to maintain a constant voltage signal across the sensor. A series of reference resistors convert the resulting sensor current to a voltage. A microcontroller reads the voltage with an A/D converter, calculates sensor resistance, and converts the resistance to temperature by table interpolation (requires a CalCurve™ for temperature conversion). The sensor excitation voltage is reversed each reading to compensate for thermal voltages and offsets.

More information about the temperature transmitters...