Non-Invasive Clamp Sensor

Temperature is one of the most frequently measured variables in process industries. Process industries where there is fluid flow inside pipe, accurate temperature measurement is crucial for process control, industry automation and safety. Most commonly used method for these temperature measurements in process industries are invasive type technique, which is popular because of accurate temperature measurement but it come with many challenges in implementation.

Conventional sensors and their associated problems

There are two popular conventional sensors to measure the temperature of process medium inside a pipe/tube. One is conventional invasive type of sensors (which are RTDs or thermocouples sensors with or without thermowells); other is conventional non-invasive surface mount sensors. Although invasive temperature sensor gives high accuracy in temperature measurements but it comes with many drawbacks such as:-

• Disturb the continuity of the pipe/tube – as installation required drilling of the process tube and there is chance of leaking at high pressure
• Installation difficulty and high down time – Based on the fluid present in the process medium there is requirement of the Thermo-well with appropriate material to protect the temperature sensor from the contamination. Thermo-well installation requires complex design consideration, if not considered results in severe consequences. Whether thermowell used or not invasive temperature sensor installation take very long time.

Although Thermo-well protects the temperature sensor from external process medium but it may cause problem in regular fluid flow.

• There are chances of breakage of Thermo-well/Sensing element in case sudden high flow rate of process medium fluid in pipe/tube.
• At the time of maintenance invasive sensor also cause problem in pipe/tube cleaning.

Many of the above mentioned problems of invasive sensors can be eliminated by using conventional non – invasive surface mount temperature sensors. But it comes with the problem of not being able to represent the accurate temperature of the process medium fluid inside pipe/tube.

Let’s look into the cause of the problems :

The conventional non invasive sensor eliminates all the major problems of invasive temperature sensors but at the cost of not being able to reflect the actual temperature of fluid inside the pipe/tube. The solution of this problem can be found by looking deep into its cause. Consider the following two concepts to better understand the cause of this problem.

• The principle of thermodynamics say that when a surface is in contact with a different temperature medium then in a steady state the surface will stabilize at a temperature whose value will be in between the two different temperature of the medium, following the heat transfer between this medium from higher energy level to lower energy level.
• Temperature sensors always measure its own temperature.

Keeping these two concepts in mind and considering different temperature mediums are actual fluid flowing inside the pipe at temperature Tin and ambient at temperature Tamb. The surface between these medium is a layer of pipe/tube material, which will be at temperature say Tm (Tamb<Tm<Tin , true when Tin>Tamb) at steady state and as the conventional surface temperature sensor is in contact of pipe material it will read temperature Tm which is not the true temperature of fluid medium. Even when it is try to modify this temperature reading to represent the actual fluid temperature by using some uniform correction factor lost its cogency in case of change in ambient and fluid temperature difference.

Conventional non invasive surface temperature sensor measures the pipe surface temperature and does not counter or compensate for the temperature difference between the fluid in the pipe and ambient which result in incorrect temperature representation by this type of sensor.

Solution Provided By Tempsens (tn Clamp Sensor) :

Heat flow between fluid and ambient through pipe/tube surface is proportional to the temperature difference between these two medium and also depends on the type as well as thickness of pipe/tube material used. Tempsens instruments’ research and development team use this concept to develop India’s first non invasive clamp sensor to accurately measure the fluid temperature inside a pipe by just clamping its sensor onto the pipe/tube. Our TN Clamp sensor uses a heat flux sensor, a RTD and an algorithm to measure the fluid temperature inside a pipe. It is equipped with a simple clamping arrangement which make it a plug and play type sensor that require almost zero installation time. Standard TN Clamp sensor come with 4-20 mA analog output, other analog output option available are 0-20 mA and 0-10 V.It gives stable and accurate temperature measurement upto 100 °C, in the ambient temperature range of 0 – 40 °C.

Applications : TN Clamp sensor can be installed without shutting down the process. Harsh process medium where it is not desirous to penetrate the process pipe/tube to install the temperature sensor, TN Clamp sensor give our customer a great alternative. It can also be used to verify the preinstalled invasive sensor, or install where new temperature measurement point is required in your industry. Other application includes small (O.D of pipe) pipeline, high viscosity fluid, high velocity fluid flow, or fluid having large particle size.

Some of the industries where our TN Clamp sensor founds its applications are:

• Oil and Gas
• Food and Beverages
• Chemical and Petrochemical industries
• Refinery