This guide with outline how to design and define a custom temperature probe.

Cable length

Determine the ideal cable length for a comfortable and easy connection from the media into the equipment.

Sometimes requesting a longer cable length can make the temperature probe more versatile for slightly different field connection conditions.

remember that it is easier for installers and stock organisation to order a longer length to achieve all variations of distance (within reason) and to cut down as required rather than to stock specific cable lengths for different cable runs.

The diagram below demonstrates the terminology and drawing example of a temperature probe. The element inside the capsule can be a Thermistor RTD or Digital temperature sensor

 

Temperature range

The temperature range is a crucial factor to provide for a custom temperature probe because it will affect the selection of capsule and type of cable.

 

Temperature Element

There are 3 main types of temperature elements ranked in order of popularity.

• Thermistor NTC or PTC (Normally NTC)
• RTD PT100 or PT1000
• Digital temperature sensor, these can vary on type of protocol.

The required element is a fundamental factor when building the custom temperature probe. It underpins the technology used to calculate the temperature so is a necessary detail.

This will be defined by the device reading the temperature. The input to this temperature reader will specify the type of sensor required.

Specifics of the element

This part typically relates to replacing a legacy temperature probe for retro fitting with equipment. 

If this is not the case the part number of the temperature sensor element is as crucial because the specifications and characteristics of the thermometer element are known.

The part number of the element can be an easy or a difficult factor to define.

RTD

If it is and RTD sensor it will be a PT100 or PT1000. It is easy to determine which one it is with a quick rest of the resistance, if the reading is in the hundreds, it’s a PT100 if in the thousands it’s a PT1000.

For an RTD temperature element the below points need to be considered

• Accuracy class
• PT100 or PT1000
• Wire connection e.g. 2 wire 3 wire 4 wire

 

Thermistor

This requires an entire section to itself as the nominal resistance at 25 degrees Celsius can vary with different models.

For a custom  thermistor element probe  the following needs to be defined

• Resistance at 25 degrees C
• Beta value common examples are 3977K 3435K
• Accuracy
• NTC or PTC

NTC resistance increases as temperature decreases.

PTC resistance increases and temperature increases.

 

Digital temperature element

To use a digital temperature element the points below will need to

• Part number
• Protocol

Common digital temperature probe protocols are I2C , One wire, SPI and RS485

• Wiring detail