Microprocessor Based Temperature Controls and Controllers
Temperature control is essential for the best productive use of your electric heaters. One of the biggest advantages of electric heat is the ability to precisely control the heater output to match the work demand
There are 3 basic temperature control devices, and each of these devices has a wide range of features and options:
- bulb and capillary - mechanical action
- surface mount - differential expansion
- electronic, microprocessor based controls
Bulb and Capillary
Bulb and Capillary Controllers have a sensing bulb at the end of a small capillary tube. A liquid expands and contracts with temperature change in the sensing bulb. The capillary tube transmits the force created by the liquid volume change to a bellows assembly. The set point determines the amount of force required to make the mechanical contact snap from and open, or closed, position to the opposite position. He amount of force required to make the action happen determines the controls differential. The differential is typically + -5% of the scale range.
These controls are rugged, durable, and come with high current carrying capacity. Typical temperature ranges and currant ratings are:
Temperature Ranges
- -16 to 40°C (0-100°F)
- 10 to120°C (50-250°F)
- 70 to 280°C (160-540°F)
- 160 to 370°C (320-700°F)
Power Ratings
- up to 240 volts, 25-amp single pole, single throw (SPST)
- up to 240 volts, 25-amp double pole, single throw (DPST)
- up to 600 volts, 15-amp triple pole, single throw (TPST)
Surface Mount
The B-1200 temperature control is a small, but sensitive temperature control. The slow make and break action of the bi-metal strut assembly gives you excellent repeatability. Once set this device will precisely maintain your temperature.
Electronic - Microprocessor Based Controls
Electronic controllers offer the widest range of temperature controller available. From open circuit board, non-indication, on-off units to full scale, dual indication fully programmable PID units. Combining these controllers with mercury contactors, solid state relays, (SSR's), or silicone controlled rectifiers (SCR's) allow you to have precise temperature control, regardless to the number of kilowatts used to heat your process.
Common Control Nomenclature for Bulb and Capillary, and surface mount controls:
- opens on temperature rise - the contacts are non powered and mechanical force opens and closed the contacts, used to control heating loads
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- closes on temperature rise - the contacts are non powered and mechanical force opens and closed the contacts, used to control cooling loads, or energize an over temperature alarm
- differential - number of degrees required to make contacts change position
- remote mounted -can only be remotely mounted to the length of the capillary tube, usually 7 feet
Common Control Nomenclature for Electronic temperature controls:
- PID -proportional, integral, derivative - matched the rate of heat output to the system demands and reduces the amount of initial overshoot
- NO contact -normally open contact, energy required to close it and keep it closed
- NC contact - normally closed contact, energy required to open it and keep it open
- J, K, R, S. T -Instrument Society of America (ISA) thermocouple designations
RTD - resistance temperature detector
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