The unseen hidden danger: the culprit behind inaccurate temperature measurements—loose wiring.

In the complex environment of industrial production, the accuracy of temperature measurement directly affects product quality, production safety, and enterprise efficiency. Among the many factors that cause abnormal temperature measurements, loose wiring or poor contact is one of the most common and easily overlooked problems. Today, we will delve into the interference mechanism of this "invisible killer" and its countermeasures.

I. How Loose Wiring Interferes with Temperature Measurement

When wiring becomes loose or has poor contact, it first leads to an increase in the resistance of the measurement circuit. A Pt100 platinum resistance thermometer has a resistance of 100Ω at 0℃, and the resistance increases by only about 0.385Ω for every 1℃ increase in temperature. This means that even an extra 1Ω of contact resistance can cause the measured temperature to be approximately 2.6℃ higher than expected.

In actual industrial environments, due to vibration, thermal expansion and contraction, etc., loose wiring can cause the resistance value of the measurement circuit to become unstable, resulting in temperature fluctuations or jumps. On a trend graph, the temperature curve will show many "gaps" instead of a smooth curve.

More seriously, when a completely loose connection leads to a poor connection or open circuit, the DCS screen may display "dead pixel" or "infinite," causing misjudgments in the control system and even equipment malfunctions.

II. Deeper Hazards of Loose Wiring

Safety Hazards: Increased resistance at the loose point can cause localized overheating under energized conditions. Tests show that when the contact resistance exceeds 5Ω, the local temperature can reach over 150℃ after one hour of energization, easily leading to junction box carbonization or even fire.

Production Risks: A chemical plant experienced a production line out of control due to a broken C-phase wire in a thermal resistor, ultimately resulting in a million-unit production stoppage. More seriously, if the temperature measurement point involves interlocking protection, it could trigger an erroneous system shutdown, causing huge economic losses.

Data Distortion: Poor contact can cause the Pt100 to switch between three-wire and two-wire systems, and the two-wire system cannot eliminate the influence of lead resistance on the measurement. In some cases, this can lead to a measurement deviation of nearly 20℃, severely affecting the accuracy of process control.

III. Analysis of the Causes of Loose Wiring

Environmental Vibration: In vibrating areas such as fans and pumps, loosening of screws after long-term operation is a common phenomenon. Data shows that the failure rate due to loose connections increases by more than 60% in vibrating environments.

Thermal Expansion and Contraction: Temperature changes cause repeated expansion and contraction of metal wires and terminals, gradually loosening the connection points.

Oxidation and Corrosion: In high-temperature and high-humidity environments, terminals are prone to oxidation, and even fixing screws can rust and fall off, further exacerbating poor contact.

Improper Installation: Failure to reach the specified torque or use of unsuitable washers during installation can also create hidden dangers for future loosening.

IV. Prevention and Remedial Measures

Prevention Strategies:

Precise Installation: Use a calibrated wrench to tighten terminals to the specified torque (0.5-0.8 N·m) and mark with red paint for later inspection.

Vibration-Proof Design: Install silicone damping pads in vibrating areas and provide a buffer bend in the cable (radius > 5 times the wire diameter).

Regular Inspection: Monthly inspection of the junction box for signs of oxidation and screw markings; quarterly infrared scanning of the junction box temperature.

Environmental Protection: In humid environments, use a double seal of silicone sealing ring + waterproof sealant; in high-temperature areas, install a heat-dissipating aluminum sleeve.

Handling Solutions:

Safety Isolation: Obtain a maintenance ticket, disengage interlock protection, and prevent malfunctions.

Power Off Verification: Disconnect the signal circuit power supply; confirm no voltage with a multimeter; live operation is strictly prohibited.

Layered Inspection: Remove the oxide layer, apply conductive grease, and re-tighten to the specified torque.

Circuit Verification: Use a precision resistance box to simulate the input; the verification display error should be ≤0.5%.

Root Cause Rectification: Install vibration damping brackets in the vibration area to fundamentally solve the problem.

Technical Innovation Solution: An improved wiring method is to connect the two leads provided with the Pt100 to the same terminal in parallel. This ensures that even if one lead solder joint comes loose, the cable resistance value will not significantly affect the actual temperature measurement, with a maximum deviation of only 1-2℃. V. Comprehensive Solutions from Hequan Instrument Technology

Addressing the industry pain point of loose wiring, Hequan Instrument Technology has launched the PT100 anti-vibration series, specifically addressing the inherent defects of traditional RTDs:

Triple-locking terminal structure: Utilizing a triple-locking design of spring washers, toothed washers, and self-locking nuts, it achieves zero loosening in a 50Hz/2mm amplitude vibration test, extending product lifespan by 3 times.

Stress relief technology: Adding titanium alloy stress rings to the armored terminals reduces the risk of bending fatigue fracture by 70%.

Intelligent monitoring function: The new generation of RTDs integrates an IoT monitoring module, transmitting contact resistance and temperature data in real time. It provides a 7-day advance warning of loosening risks and automatically triggers maintenance work orders via PLC.