Platinum SMD Sensor Elements

The current self-heating effect in a platinum sensor element has to be carefully considered to avoid errors in temperature measurement.  Applying too much measuring current to a Pt100 or Pt1000 element will result in it warming up by an amount that will create an offset between the exact temperature and the element temperature.

Each element datasheet shows a value for this self-heating in K/mW and it also shows a value for the maximum measuring current that should be applied.  As this self-heating value is determined at 0°C, it is not representative of many applications the sensor will be used in.  So it should be primarily used to compare between different element types.

Also if you put the platinum element inside a probe, then the extra thermal mass helps to effectively lower the self-heating value.  Conversely if you use a platinum sensor in a full or partial vacuum, then the self-heating value can increase due to the reduced thermal conductivity of the surrounding medium.

Finally self-heating can be used to good effect in air-flow measurement applications where two platinum elements are used together in a comparator network.  One is self-heated and the other acts a reference sensor, so that the airflow over the self-heated element can be measured by a calculation derived from experimental observation.

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The temperature coefficient, also referred to as the “alpha value”, is the average change in resistance between 0 and 100 °C, and calculated using the formula.

Where R100 is the resistance at 100°C and R0 is the resistance at 0°C.

YAGEO NEXENSOS supplies Thin Film Platinum RTD Elements with the following temperature coefficients:

3850ppm
3750ppm (Pt1000 only)
3770ppm (Pt200 for automotive application only)

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For a new application, we typically recommend the YAGEO Nexensos M222 type (2.3mm L x 2.1mm W). The M222 has a relatively low unit price, and will fit in a variety of probe sizes. For existing applications, a larger size element, such as the M1020 (9.5mm L x 1.9mm W) may be required to match an existing size footprint.

The following table summarises some size dependent properties.

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Our YAGEO Nexensos Thin Film Elements differ primarily by their operating temperature range.

The table below summarises the various types.  It is important that the min/max operating temperature of your application falls within the operating range specified. Using a part outside the rated operating range may produce unpredictable results.

For detailed information please see individual data sheets on our website or call our engineers on 01606 871680.

Thermistors, thermocouples and RTD Sensors are all used to measure temperature. However, in particular circumstances when greater precision, coupled with longevity and stability are required ATC Semitec recommend a Pt100 (Resistance Temperature Detector) should be used.

RTDs give excellent linearity across a wide and high temperature range. This means that as the resistance increases the temperature also increases and therefore can be measured.  In comparison to thermistors and thermocouples their stability reduces above certain temperatures.

Based on high precision, accuracy, stability and longevity Pt100, Pt1000 are ideal for use, and frequently used in the following applications:

HVAC

Automotive (Measuring engine temperature, oil level sensors, intake air temperature)

Consumer Electronics

Food handling, processing

Medical Electronics

Military

Aerospace

Other industrial processes

In these situations, it is recommended that a Platinum RTDs is used as it offers the most stable resistance/temperature relationship compared to Nickel or Gold RTDS.

For help with identifying the correct PRTD for your application contact our technical engineers at ATC Semitec on 01606 871680

The type of platinum element to be used is usually guided by the requirements of the specific application.  The size of the sensor it needs to fit inside, the temperature range to be measured and the accuracy of the element are the key parameters.

Thin-film elements are intrinsically vibration-resistant and lower in cost than wire-wound elements, so thin-film elements meets the needs of the majority of temperature sensing applications.

Wire-wound elements can offer smaller sizes, cylindrical formats and much higher levels of accuracy, e.g 1/5thDIN (W0.06) and 1/10thDIN (W0.03).

The following table summarises the advantages of each type:

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Pt100 temperature sensors are platinum sensor elements with a resistance of 100ohms at 0°C.  The Pt100 is a temperature sensor in which the resistance changes linearly with temperature.  Therefore, by simply measuring a sensor’s resistance, the Pt100 can be used to measure temperature.

Thin-film Pt100 sensors are manufactured by depositing a thin layer of high purity platinum onto a ceramic substrate in clean room conditions.  A pattern is then etched onto the element, thus creating the electrical circuit. They are then terminated and sealed with a glass coating, which accounts for their very long term stability and durability.

They are a very popular choice across many different industries due to their characteristics of long-term stability, linearity, accuracy and repeatability.

Whilst the Pt100 is the most common sensor, other variations are available, and the notation used is as follows;

“Pt” followed by a number (say 100), refers to the resistance value at 0°C. Ro resistance values available are 100 ohms (Pt100), 200 ohms (Pt200), 500 ohms (Pt500), 1000 ohms (Pt1000), 2000 ohms (Pt2000) and even 10000ohms (Pt10000).

Have a question or need a sample ? Call one of our engineers today on 01606 871680