TWI-PH1: Loop-Powered Two-Wire pH to 4-20mA Converter/Isolator  specsheet 

  • High Input-Output-Power Isolation (800VAC Test)
  • Small Size - Fits Standard Explosion Proof Housing
  • Industry Standard 4-20 mA Output
  • Input Impedance > 1E12 Ohms
  • Temperature Compensated
  • Loop-powered from Input Loop, no Additional Power Supply Required
  • Wide Operating Range (12 to 60 VDC)
  • High Noise Rejection
  • CSA and NRTL Approved (LR 51078)


The TWI-PH1 is an isolated two wire pH transmitter in a small, easy to install package. It has easily accessible screw terminals and is built in a rugged housing. A standard BNC connector allows direct plug-in of the pH probe.

The TWI-PH1 consists of a pH signal conditioner complete with temperature compensation and an isolator. The temperature compensation is accomplished by means of a 3 KOhm thermistor. The isolated output prevents interaction between output signals if more than one pH transmitter is used in a system.

  • Isolation: Input to Output to Power 800 VAC (test)
  • Operating Power (from Output Loop): 12-60 VDC
  • Output: 4-20 mA
  • Range: 0-14 pH
  • Accuracy/Linearity:+/- 0.01 pH
  • Operating Temperature: -20 Deg.C. to +50 Deg.C.
  • Temperature Compensation: 3KOhm Thermistor
  • pH Probe Connector: BNC
  • Line Effects: 0.03% per 10 VDC Line Change (calibrated for 24 VDC)