Using Sensors to Measure Engine Oil Temperatures

Topics Covered

Introduction
What Kind of Sensor is Right for Engine Oil Temperature?
Three Choices for Measuring Engine Oil Temperature
Hermetically Sealed RTD Sensors (HSRTD)
Hermetically Sealed Thermistor Sensors
Hermetically Sealed Thermocouples

Introduction

Engines are considered to be complex pieces of machinery and thoroughly testing them means testing many different variables. How much air is the engine taking in? How’s the noise level?

Is the fuel combusting properly?

All these measurements need specialist equipment. However, the trickiest to measure is oil temperature.

It is essential to control engine oil temperature since it has a particular working range. If it is too cold, the engine will fail to be properly lubricated. If it is too warm, the viscosity of the oil will be reduced- and again the engine will suffer.

Oil temperature is also expected to change based on how hard the engine is working. Thus, it is necessary for the measurement to be continuous.

What Kind of Sensor is Right for Engine Oil Temperature?

The type of sensor needed for this job must comprise of three closely-related qualities:

  • Submersible – The sensor should be designed to measure temperature while submerged in oil
  • Hermetic – The sensor must be hermetically sealed (air-tight), in order to prevent any interaction with the oil
  • Protected –The sensor should be able to remain submerged in oil indefinitely without malfunction since continuous readings are needed.

It is also essential for the sensor to be flexible enough so it can be inserted deep into a duct where it can reach the oil. This makes popular rugged equipment such as thermowells and metallic industrial probes unsuitable. These devices would not be affected by chemical alteration by the engine oil, and they are not flexible enough for use inside an engine oil duct.

Three Choices for Measuring Engine Oil Temperature

In order to offer a straightforward solution, Omega Engineering has developed three types of specialist probes for this application. Each integrates a popular type of temperature sensor: thermocouple, thermistor or RTD sensors.

The probes are perfect for measuring engine oil temperature, being:

  • Compact and flexible enough for use in small spaces, with no enlargement at the sensor tip
  • Hermetically sealed with PFA insulation, producing an electrically isolated device that is highly resistant to oils
  • Easily cleaned or sterilized

All three probe types ship with stripped ends as standard.

Hermetically Sealed RTD Sensors (HSRTD)

The HSRTD range of hermetically sealed RTD probes has been built around the popular PT100 platinum-based sensor. RTDs offer exceptional stability, linearity, accuracy and chemical resistance.

Range options include length up to 5 m, and a choice of Class 1/3 DIN, Class A and Class 1/10 DIN versions with stripped ends. A PT1000 RTD version and a -200 °C version are also available.

Hermetically Sealed Thermistor Sensors

Thermistors are among the best choices for point sensing and sensitivity, although they provide narrower temperature ranges than other sensor types. The Omega HSTH-44000 Series of hermetically sealed thermistors measure from -80 °C to +150 °C, which is ideal for several engine oil applications.

The range provides three models with specialized resistance ratings: 2k252, 5k and 10k ohm. Each model is one meter long.

Hermetically Sealed Thermocouples

Thermocouples are generally selected for their low cost, high-temperature operation and fast response times. The Omega HSTC Series of hermetically sealed thermocouples is rated to 250 °C (482 °F). Range options include Type T and Type K connector models, in lengths of 1, 2 and 3 m. Male Type T and K connector accessories are also available.

This information has been sourced, reviewed and adapted from materials provided by Omega Engineering Ltd.

For more information on this source, please visit Omega Engineering Ltd.

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