Thermocouples are temperature sensing devices that utilise the properties of two unlike metals, which have been joined at the sensing end. These instruments work by differentiating between temperature changes and this data travels through to a controller that displays temperature.
Depending on application needs, there are a wide range of thermocouple variations such as Type K, J, N and more. These all contain various a mix of metals which work in their given applications.
Adding to this, different applications also need special measurements of thermocouple dimensions, such as stem length, transmitters, length of thermocouple wire etc.
There are three types of thermocouple wire. The differences are explained below.
The first is thermocouple grade which is the wire use in the thermocouple itself upon manufacturing. This wire is highly accurate and slightly dearer than the other grades.
The second is extension grade. This is somewhat of a lower grade due to the slight impurity in the metals. As the name suggests, the extension cable is used purely to connect and extend off the thermocouple wires. The main reason for this, is so the thermocouple can connect to a temperature controller or measuring device, whilst being more cost effective than thermocouple grade wire.
The third is compensating cable. The alloys used in this cable are different to those in thermocouple wire, however, over a longer range, they produce the same millivolt reading. This cable is used when a thermocouple wire is too expensive or when there is a long length needed.
The colour coding used in Australia is ANSI M96.1 code.