The key to preventing signal attenuation in hot runner sensors lies in optimizing the signal transmission path, enhancing anti-interference capabilities, and ensuring the reliability of physical connections. The following are systematic preventative measures:
1. Use Short-Distance Wiring and Local Signal Conversion
Controlling Wire Length: Install the signal acquisition module as close to the sensor as possible, keeping the wire length within 10 meters. This significantly reduces resistance voltage drop and the risk of interference coupling.
Using 4–20mA Transmitters for Long-Distance Transmission: For long-distance transmission scenarios >30 meters, a signal transmitter module should be installed at the sensor end to convert weak voltage/resistance signals locally into industrial standard current signals. This provides strong anti-interference capabilities and minimal attenuation.
Example: In a hot runner system for injection molding machines, each temperature control zone is equipped with a miniature transmitter, uniformly outputting a 4–20mA signal to the PLC, effectively avoiding long-distance transmission problems.
2. Select High-Specification Cables and Standardize Wiring Methods
Use Shielded Twisted Pair Cables: Effectively suppresses electromagnetic interference. The shielding layer should be reliably grounded at one end (grounding resistance ≤ 4Ω) to avoid ground loops.
PT100 uses a three-wire or four-wire system: Three-wire systems compensate for the influence of conductor resistance; four-wire systems completely eliminate lead resistance errors and are suitable for high-precision temperature measurement.
Select Appropriate Wire Diameter: It is recommended to use copper conductors with a cross-sectional area ≥ 0.5mm² to reduce resistance per unit length and minimize voltage drop.
3. Strengthen Electromagnetic Protection and Installation Environment Management
Keep Away from Strong Interference Sources: Signal lines must not be laid parallel to the power lines of frequency converters, heating rods, or high-power motors; if crossing is unavoidable, they should be at a 90° angle.
Install Metal Conduit: Use galvanized steel or stainless steel conduits and ensure reliable grounding to create a Faraday cage effect, further shielding against external electromagnetic fields.
Local advice in Wuhan: High humidity during the rainy season (June–September) can easily lead to decreased insulation. It is recommended to use IP67-rated sheathed cable or regularly check the insulation resistance of the line to be >1MΩ.
4. Front-end Signal Conditioning and System Maintenance
Add low-noise amplifiers and filters: Integrate an RC low-pass filter circuit (cutoff frequency 500Hz–1kHz) at the signal input to filter out high-frequency noise interference.
Regular calibration and inspection: Perform system calibration every 3–6 months, check for oxidation and looseness of the wiring terminals, and clean or replace aging wiring promptly.
Use temperature control modules with self-test functions: Chips such as MAX31855 can monitor cold junction temperature, communication status, and CRC check in real time, providing early warning of signal anomalies.
