About multipoint thermocouple designs
Multipoint thermocouples, when designed correctly and with thought, will provide great dividends in fuel and energy savings, product uniformity, and safety, as well as the increased economy of long-lived and accurate temperature measuring instrumentation. Some of the major design requirements that should be considered when specifying these thermocouples are:
The number and point locations that will be required.
- Operating temperature range including temperature excursions.
- Operating conditions such as: pressure, corrosion, safety, leakage.
- Where and how the multipoint will enter the process.
- Are the thermocouples going to be direct immersion into the process or installed into thermowells or pipe wells?How long a life is required for these thermocouples?
- Installation and replacement difficulty, safety, and cost.
- Temperature response time.Junction design and type, and is RF a concern?
- Thermocouple calibration and accuracy.
- Protection sheath material, length, and diameter.
- Thermocouple transition to lead wire and the exit from the process.
- Lead wire length, size, flexibility, protection, and connection to instrumentation.
- Will these thermocouples be directly connected to the process instrumentation or to a transmitter?
- Traceability requirements, calibration requirements, and in process calibration verification.
- Very often the choice of temperature control or monitoring instrumentation is the last step in process design.
- Significant savings can be achieved if the most appropriate technologies are selected from the outset.
- Multi measuring point process control thermocouples will provide fuel and energy savings, product uniformity and safety.
Pre-planning multipoint thermocouple designs will pay large dividends
By A Brown, Temperature Controls
Electricity+Control, November 2011 (pgs 86 – 88)