Temperature has an effect on all analytical measurements. For this reason, nearly all Hamilton sensors have temperature compensation. Temperature compensation comes in the form of a small resistance-based temperature element imbedded within the sensor. This article details the types of temperature elements along with some basic information about applying temperature compensation in your applications.
Common Temperature Sensor Types
PT100 - PT100 RTDs use a platinum element and produce 100 ohms at 0C. The element provides increasing resistance with temperature, thus at a typical ambient room temperature of 25C the resistance will be around 110 ohms. PT100 RTD elements are an option with Hamilton analog pH sensors.
PT1000 – PT1000 RTDs also use a platinum element which produces 1000 ohms at 0C. At room temperature the resistance is around 1097 ohms. PT1000 elements are found on Hamilton analog conductivity sensors, certain ORP sensors, and optional on Hamilton pH sensors.
NTC Thermistors – NTC thermistors are resistance based temperature elements that provide a decreasing response to increasing temperature. Hamilton uses the NTC 22 kohm thermistor element in all sensors with Arc technology as well as our optical dissolved oxygen sensors. These temperature elements output 22 kohm at an ambient temperature of 25C.
Which sensor do I use?
The type of sensor may actually be influenced by the control system or transmitter that the sensor is being connected to. For instance, most pH transmitters will have several options for either PT100, PT1000 or several other temperature inputs. The selection of the temperature input in the transmitter must match the temperature element within the sensor for temperature to be displayed correctly. Some transmitters will auto-detect the temperature sensor based on the measured resistance which makes switching between sensors with different temperature elements very simple. Finally, Arc sensors have a built-in microtransmitter at the sensor which performed the temperature compensation within the sensor so that the 4 to 20mA analog or Modbus output signal is already temperature compensated and no further corrections are needed.