How to Design a Hot Runner Multi-Sensor Average Value Control System

A hot runner multi-sensor average value control system should be designed using a defined procedure that includes "scenario selection → hardware layout → calibration and debugging → maintenance mechanism." Improving temperature measurement accuracy and mitigating localized frictional heat interference are the main goals. The following are the whole design steps:

1. Initial Scenario Selection and Verification of Requirements

To prevent forcing a design that can cause further issues, first ascertain whether the solution is applicable:

Applicable Scenario Determination: Designed exclusively for large-flow, high-shear molds with a single hot runner channel diameter of at least 8 mm and high-precision requirements (medical/automotive precision parts); for small-sized runners (less than 8 mm), prioritize single-point sensor position optimization and avoid using this solution.

Accuracy Requirement Matching: A weighted average control logic must be created for precision injection molding, but a straightforward arithmetic average is adequate for standard injection molding.

Verify Hardware Compatibility: Determine whether current temperature controllers accept multi-sensor input natively; set aside room for older systems' expansion and retrofitting beforehand.

2. Design of Hardware Systems

(1) Selection and Pairing of Sensors

To guaranty consistent specifications, give priority to K-type thermocouples or PT100 RTDs of the same batch and model; calibrate in a constant temperature oil bath upon arrival at the plant, choosing sensors with a mutual variation ≤ ±0.5℃ for pairing and removing those with excessive deviation.

(2) Design of Installation Positions

Each channel only requires two sensors (three sensors are expensive and provide little advantage). Create in accordance with the differentiation principle:

Requirements for Sensor Position Design Allocation of Weights (Weighted Average Mode)

Middle Section of the Main Channel

To prevent conductive heat, choose a low shear zone that is 20–30 mm from the nozzle tip and ≥5 mm from the heater.

60% to 70%

Cavity End on the Nozzle Side

≥8 mm from the high shear nozzle edge, near the melt discharge area

30% to 40%

General Design Requirements: Installation depth and channel location in multi-cavity molds must be perfectly symmetrical, with errors regulated within ±1mm; two sensors must be spaced at least 10mm apart to prevent thermal interference. (3) Design of Wiring To minimize signal interference and prevent parallel operation with power lines, all sensor signal lines are routed in separate cable trays using twisted-pair shielded cables. To prevent wiring confusion, every sensor in every channel is numbered consistently and linked to the appropriate input port of the temperature controller.