Workpiece temperature is the temperature of the part being heated. Cartridge heater sheath temperature is the temperature at the heater’s outer surface. A controller setpoint is the target entered into the control system. These describe different things and should be identified separately in a heater specification.
A heater transfers heat through its installation into the workpiece. Temperature readings depend on where the sensor is placed, the operating stage and the heat transfer conditions. A reading inside a heater, at its surface or in a workpiece should be labeled with that location.
For example, an application may specify a required temperature at a point in a heated block. That requirement alone does not tell the supplier the temperature of the heater sheath or the conditions at its lead exit.
The controller acts on the signal from its connected sensor. The relationship between that reading and the process area depends on the sensor location and the equipment. A stable controller display does not establish that the entire workpiece has a uniform temperature.
Specify the location where the process requirement applies. If uniformity matters, define several measurement points, the operating stage and the permitted temperature difference.
A brief temperature peak and continuous operation place different requirements on a design. Include the required hold duration, heating and cooling periods and cycle frequency. When sharing a test result, state the operating history rather than reporting only the highest observed value.
A fixed temperature offset cannot describe every cartridge heater installation. Hole fit, contact conditions, power input, workpiece geometry and heat loss affect the temperature distribution. Changing the installation can change the relationship between measurement locations.
Use measurements and a review of the actual application rather than applying a temperature difference from unrelated equipment.
For each temperature requirement or measurement, record:
Keep lead and connection temperature requirements separate as well. A workpiece requirement does not establish a suitable sensor, lead material or termination.
Two products advertised with the same temperature number may be describing different measurements or operating conditions. Ask what the number refers to before treating the products as comparable.
For an existing machine, provide the current drawing or part reference and the actual workpiece requirement. Explain where the temperature is measured and which operating conditions need to be reproduced.
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