In modern bulk material conveying systems (mining, ports, power generation, metallurgy, cement and similar industries), belt conveyors are the core equipment for continuous material transport. However, due to overload, material accumulation, insufficient belt tension or pulley wear, relative sliding between the conveyor belt and the drive pulley (known as belt slip) occurs very easily. If slipping is not detected in time, severe friction will cause serious wear of the conveyor belt, local overheating and even fire, resulting in huge production losses.
The XLDH-I Contact Type Belt Slip Detector (Speed Switch) is a high-reliability safety protection device designed specifically for industrial-grade belt conveyors. This article provides an in-depth analysis of its working mechanism, core performance advantages, standard installation procedure and electrical integration solutions.
1. Working Principle and Core Mechanism of the Contact Type Belt Slip Detector
A contact type belt slip detector acquires real-time speed by means of a mechanical contact wheel that touches the non-working surface (or the belt edge) of the conveyor belt directly.
When the conveyor is running, the moving belt drives the die-cast contact wheel of the slip detector by friction. The rotation of the contact wheel drives a high-precision photoelectric sensor through the internal transmission shaft, generating pulse signals that are transmitted in real time to the counting unit of the built-in ARM embedded microcontroller (MCU).
The ARM processor performs high-precision calculation and speed comparison on the continuously incoming pulse frequency:
- Normal operating state: the contact wheel speed is consistent with the designed linear speed of the conveyor belt, and the controller outputs a normal signal.
- Slip fault state: when the belt slips and its linear speed drops, the contact wheel speed decreases synchronously. As soon as the belt speed drops by 50% compared with the normal set speed (factory preset threshold), the ARM MCU responds quickly, the internal relay operates and the switch signal output is triggered.
This switch signal can be connected directly to the on-site PLC control system or interlock circuit to achieve stall emergency shutdown and on-site audible and visual alarm, eliminating belt tearing and fire hazards caused by continuous slipping at the source.
2. Structural Features and Protection Advantages of the XLDH-I
The XLDH-I adopts an integrated dust-proof and waterproof structural design, purpose-built for harsh mining and outdoor working conditions:
- High-strength die-cast aluminium alloy housing: extremely strong resistance to impact and mechanical vibration; the housing surface is treated by high-voltage electrostatic plastic spraying, giving excellent resistance to acid and alkali corrosion.
- IP67 high sealing protection: ageing-resistant sealing rings are fitted at the housing joints, effectively preventing dust ingress and powerful water jet erosion; suitable for 0~95% relative humidity and an extreme working temperature of -40℃~50℃.
- Elastic contact wheel pressing structure: the contact wheel surface features deep anti-slip teeth, combined with a torsion spring/spring retaining mechanism, ensuring that the contact wheel always fits tightly against the belt when the belt fluctuates up and down and avoiding false operation caused by jitter.
- ARM microcontroller core: compared with traditional centrifugal or simple analog circuit detectors, the ARM MCU offers fast response, small calculation error (<1%) and strong anti-electromagnetic interference capability, and has a built-in 10-second start delay (Start Delay) function that automatically bypasses false alarms during the acceleration phase right after the conveyor starts.
3. Core Technical Parameter Comparison Table
To facilitate engineering selection and system integration, the key electrical and physical parameters of the XLDH-I contact type belt slip detector are as follows:
| Parameter | Specification |
|---|---|
| Working Voltage | AC 220V (50/60Hz) |
| Power Consumption | ≤ 3W |
| Detection Range | 10 ~ 9999 R/min |
| Alarm Threshold | Belt speed drop of 50% (factory setting) |
| Start Delay | 10 seconds (automatically bypasses the start-up process) |
| Output Mode | 1 × SPDT single-pole double-throw relay |
| Contact Rating | AC 250V 3A / DC 30V 3A |
| Optimum sensing distance of the sensing head | 10 mm |
| Protection Level | IP67 |
| Ambient Temperature / Humidity | -40℃ ~ +50℃ / 0 ~ 95% RH |
| Pressure Range | 80 kPa ~ 110 kPa |
| Applicable Belt Width | B = 650 mm ~ 1200 mm |
4. Standardized Installation Procedure and Position Specifications (Belt Width 650~1200 mm)
Correct physical installation is the prerequisite for ensuring long-term stable operation of the slip detector. For belt conveyors with a belt width of 650 mm to 1200 mm, please strictly follow the steps below:
Safety Warning (WARNING)
- Live working is strictly prohibited: before installation, wiring or maintenance, the main power supply of the conveyor must be switched off and locked out with a tag.
- Note on non-explosion-proof products: the XLDH-I is an ordinary industrial protection product and must never be used directly in environments with high-concentration gas or flammable and explosive gases.
- Reliable grounding requirement: the housing grounding terminal must be firmly connected to the on-site protective earth (PE), otherwise the device will lose its internal lightning and surge protection capability.
Installation preparation materials
- XLDH-I slip detector body (including contact wheel and fixing bracket)
- Dedicated crossbeam mounting bracket, 1 set
- M10×35 fasteners, 2 sets
- U-bolts, 2 sets
Detailed installation steps
- Fix the mounting bracket: use the U-bolts to fix the mounting bracket on the conveyor longitudinal beam (H-beam or channel steel); do not fully tighten the nuts at this stage so that fine adjustment remains possible later.
- Install the detector body: fix the slip detector onto the bracket mounting plate with M10 bolts.
- Calibrate the parallelism and perpendicularity of the contact wheel:
- Parallelism: adjust the bracket position so that the rotation axis of the contact wheel is perpendicular to the running direction of the conveyor belt, and the rolling direction of the contact wheel is strictly parallel to the running direction of the conveyor belt.
- Perpendicularity: adjust the bracket height and angle so that the support arm of the slip detector remains perpendicular to the plane of the conveyor belt.
- Pressure and elastic range setting: adjust the installation height so that the contact wheel presses against the conveyor belt and compresses the spring by 10~15 mm, keeping it within the elastic tension range and ensuring that the contact wheel does not leave the belt surface when the belt jitters under full load. Finally tighten all U-bolts and nuts.
5. Electrical Wiring Principle and Control System Integration
A 6-core high-flexibility double-shielded cable (colour marking: red, yellow, black, blue, brown, white) is led out from the rear of the XLDH-I detector. Please refer to the following definitions when wiring:
Cable core definitions
- Brown (BN) & Blue (BU): AC 220V working power supply input.
- Black (BK) & Red (RD): normally open contact (NO). It stays open while the conveyor runs normally and closes when a slip alarm occurs.
- Black (BK) & Yellow (YL): normally closed contact (NC). It stays closed while the conveyor runs normally and opens when a slip alarm occurs.
- White (WT): housing safety grounding wire (GND).
System integration recommendations
- PLC logic control: lead the black and red (NO) wires into the PLC digital input module (DI). When the signal closes, the PLC program, after 1~2 seconds of software filtering, issues a "conveyor slip / stall" fault command, cuts off the main motor relay and triggers the alarm.
- Direct hardware interlock: connect the black and yellow (NC) in series in the control circuit of the main motor contactor. Once slipping occurs, the contact opens and directly cuts off the contactor coil to achieve physical shutdown.
6. Routine Inspection, Maintenance and Common Troubleshooting
In order to extend the service life of the slip detector, it is recommended to establish a regular maintenance mechanism:
- Weekly physical inspection:
- Check whether the teeth on the contact wheel surface are blocked by foreign objects or severely worn.
- Check whether the contact wheel keeps tight contact with the belt surface and whether the spring tension is normal.
- Monthly tightening and cleaning:
- Check whether the nuts of the mounting bracket and U-bolts have loosened due to conveyor vibration.
- Clean the dust and material accumulation on the housing and at the cable outlet to ensure heat dissipation and sealing performance.
- Common fault diagnosis:
- The belt runs normally but false alarms occur frequently: check whether the contact wheel has left the belt surface (spring loosened) or whether the wiring cable has poor contact; check whether the lightning protection grounding is sound.
- The belt slips but the detector does not alarm: check whether the contact wheel bearing is jammed, causing friction failure; check whether the ARM controller supply voltage is normal (AC 220V ±10%).