I. Core Selection Solution (Low-Cost Alternative)
Maker-Grade Magnetostrictive Displacement Sensor: The total cost is approximately 150 RMB, and it is based on a self-made Arduino development board and an open-source 3D model. The measurement accuracy is at the millimetre level, making it appropriate for hot runner displacement monitoring scenarios with a range of up to 1 metre.
Use a parsimonious linear displacement sensor that is domestically produced and priced at approximately 80-120 RMB per unit as an alternative low-cost solution. It directly adapts to existing SCADA systems, requires no sophisticated self-development, and supports analogue signal output.
TIPS FOR AVOIDING: It is advisable to refrain from purchasing displacement sensors from imported brands that are of high quality. Their performance is excessive for hot runner thermal expansion displacement monitoring scenarios, and their unit price can easily reach thousands of RMB.
II. Procedures for Hardware Installation
Utilise open-source 3D printed components to construct a sensor mounting bracket, ensuring that the layer thickness is 0.1mm. After installation, verify that the sensor is parallel to the heated runner plate's side with a coaxiality deviation of no more than 0.1mm.
The sensor body was affixed to the non-moving side of the mould template, with the measuring probe faintly touching the non-sealed side of the hot runner manifold. This allowed for an initial compression of 0.5mm.
To prevent interference from strong electrical signals around the hot runner from influencing displacement data acquisition, shielded wire was employed for wiring, with the shield reliably grounded at one end.
III. Signal Acquisition and Access
The self-made solution eliminates the necessity for an additional hardware gateway by directly utilising an Arduino to receive displacement data and transmit it to an existing SCADA industrial computer via serial port.
A 4~20m output is directly produced by the cost-effective off-the-shelf sensor.An analogue signal that connects to the current fallback AI channel of the temperature control system without necessitating an additional acquisition module.
A displacement over-limit threshold is established. The existing audible and visual alarm is promptly triggered when the thermal expansion displacement of the hot runner exceeds the preset safety clearance, thereby providing early warning and preventing potential hazards.
IV. Verification and Calibration
The sensor output value was recorded after the displacement of the hot runner plate was manually adjusted using a feeler gauge in a cold state. To guarantee a measurement error of no more than 0.1mm, a two-point linear calibration was implemented.
In order to guarantee data consistency and precise and efficient monitoring, sensor displacement data and theoretical thermal expansion calculations are simultaneously recorded during the segmented heating process of the hot runner.
This low-cost add-on solution is optimally adapted to the on-site conditions of precision injection moulding hot runner production lines. It enables real-time monitoring of thermal expansion displacement at an incredibly low cost, thereby providing early warnings and preventing potential issues from the outset.
