Hansford Sensors offer a range of temperature sensors to suit various applications. Below we look at the differences between accelerometers with integral temperature sensing RTD and Semi-Conductor Sensors.

Fig 1

Fig.1 An IC temperature sensor is an electronic component that sits on a circuit board and produces an output voltage that is proportional to absolute temperature. The sensor package is small with a low thermal mass and a fast response time. The most common temperature output is 0-1 volt proportional to 0– 100°C (-32 to 212°F) but many other ranges are available.

Fig 2

Fig.2 An RTD is a platinum resistance thermometer that offers excellent accuracy over a wide range of temperatures. The most common is a PT100 that has a resistance of 100 ohms at 0° C and 138.4 ohms at 100°C. An RTD is a sensor that can be located anywhere at the end of two cables that are then fed into a bridge completion circuit and the change of resistance measured by an unbalanced voltage.

Fig 3.

Fig.3 This is a tabulated pros and cons chart that illustrates the differences between the two technologies of semi-conductor vs RTD.

Fig 4.

Fig.4 This shows the relative positions of the RTD and semiconductor temperature sensors inside a top exit accelerometer and a side exit accelerometer. In both cases the RTD is closer to the bearing being measured. In addition the RTD is in direct metal contact with the bearing. The relative distances of the RTD and the semiconductor sensor is much less in a side exit than top exit accelerometer.

Fig 5.

Fig.5 In most applications the whole accelerometer soaks to the temperature of the bearing and the semiconductor temperature sensor measures the bearing temperature closely. However a much larger difference is seen when the accelerometer is subject to forced cooling. These forced cooling conditions can exist in cooling tower or FD fan applications.

Fig 6.

Fig.6 Temperature measurement in the sensor can be different to the temperature of the bearing. In addition temperature changes can lag behind changes in temperature of the bearing. This chart shows the relative differ-ences between RTD and semiconductor in lag and delta T. However for machine health monitoring relative temperature changes are always monitored.

Fig 7.

Fig.7 This shows the different sensitivities and different temperature ranges of the different semiconductor temperature sensors that Hansford Sensors offers. 10mV/°C is most common but 10mV/°F is available for those locations where °F are used.

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