Conveyor Protection & Speed Monitoring
Bolec SS501 Conveyor Speed Switch – Zero Speed, Belt Slip &
Overspeed Monitoring Relay
A programmable dual-channel speed monitoring switch for mining
conveyors, crushers, feeders, pumps and rotating machinery.
Detect conveyor slowdown, zero speed, belt slip, underspeed or
overspeed conditions and activate an alarm, interlock or equipment
shutdown circuit.
Dual Speed Inputs
Dual Relay Outputs
Zero Speed Monitoring
Belt Slip Detection
2–9,990 Hz
sensor inputs and independent relay outputs.
Conveyor Speed Monitoring for Safer, More Reliable Operation
Conveyor belt slip, stalled shafts and failed drive components can
cause material build-up, equipment damage and costly production
downtime. The Bolec SS501 monitors pulse frequency from a rotating
shaft, conveyor pulley, motor, gearbox or engine and changes its relay
output when the programmed speed threshold is reached.
By connecting the SS501 to a magnetic pickup, inductive sensor or
Hall-effect sensor, operators can monitor whether critical equipment
is running at the correct speed. Its relay outputs can be connected to
a warning beacon, buzzer, PLC input, control relay, solenoid or
shutdown circuit.
Detect a reduction in pulley or shaft speed caused by belt slip,
drive failure, mechanical jamming or conveyor stoppage, then activate
an alarm or interlock before further damage occurs.
High-Demand Mining and Industrial Applications
Conveyor Zero Speed Monitoring
Detect when a conveyor pulley or driven shaft has stopped while
the drive system is expected to be operating. Use the relay output
to trigger an alarm, stop upstream equipment or initiate a
controlled shutdown.
Belt Slip and Underspeed Detection
Monitor actual pulley or shaft speed and activate an output when
speed falls below the required operating threshold. This can help
identify belt slip, overloaded conveyors, worn drive components or
developing mechanical faults.
Crusher and Screening Plant Protection
Monitor crusher shafts, screen drives and rotating plant for
abnormal underspeed, overspeed or loss of motion. The independent
relay outputs can provide separate warning and shutdown functions.
Feeder, Auger and Screw Conveyor Monitoring
Detect stalled feeders, broken couplings, chain failure or loss of
shaft rotation before material flow problems affect the rest of
the production process.
Pump and Auxiliary Drive Monitoring
Monitor slurry pumps, dewatering pumps, hydraulic drives, PTO
systems and auxiliary shafts to detect loss of drive, abnormal
speed or mechanical disconnection.
Mobile Plant and Engine RPM Protection
Use the SS501 for engine overspeed monitoring, vehicle speed
interlocks, PTO protection or combined engine RPM and vehicle
speed logic on mining and heavy-duty mobile equipment.
Designed to Support Mining Reliability and Downtime Reduction
Detect loss of motion early
Identify stalled or slowing equipment before a minor fault becomes
a larger mechanical failure.
Protect conveyor systems
Monitor the actual rotating shaft or pulley rather than relying
only on whether the motor contactor is energised.
Reduce unplanned downtime
Use alarm or shutdown outputs to respond to belt slip, underspeed
or zero-speed conditions.
Monitor two speed signals
Use two independent channels for two machines, two shafts or a
combined monitoring strategy.
Integrate with existing controls
Volt-free relay contacts simplify connection to PLC inputs,
warning devices, interlocks and external control relays.
Configure the required response
Select normally open, normally closed or pulsing output behaviour
for each application.
Flexible Dual-Channel Monitoring
Dual Input → Dual Output
Monitor two separate conveyors, shafts or machines. Each input
controls its own relay output and can use its own programmed
threshold.
Dual Input → Single Output
Combine two monitored conditions into a common interlock. The
output can change state when either monitored condition reaches
its programmed threshold.
Single Input → Dual Output
Monitor one speed signal with two different setpoints or two
separate actions, such as an early warning followed by a shutdown
response.
Single Input → Single Output
Use one channel as a straightforward conveyor speed switch,
zero-speed switch, underspeed relay or overspeed switch.
each speed-monitoring channel.
relay modes and Channel 2 high-resolution operation.
Key Features
- Two independent speed or frequency-monitoring inputs.
- Two independent volt-free relay outputs.
- Programmable high and low switching points for each channel.
- Suitable for zero speed, underspeed and overspeed monitoring.
- Compatible with inductive, magnetic pickup and Hall-effect
sensors. - Onboard 10 kΩ pull-up resistors available for Hall-effect devices.
- Normally open, normally closed and pulsing output options.
- Pulsing output operates at approximately 1 Hz after the trip point.
- Channel 2 high-resolution mode for low-speed applications.
- Live frequency display for setup and fault-finding.
- Reset function restores factory-default settings.
- 12/24 VDC operation for fixed and mobile plant applications.
Technical Specifications
| Supply voltage | 12/24 VDC, negative ground |
|---|---|
| Typical current draw | Approximately 30 mA quiescent |
| Number of inputs | Two independent frequency inputs |
| Sensor compatibility | Inductive or magnetic pickup and Hall-effect sensors |
| Standard frequency range | 2–9,990 Hz per channel |
| Channel 2 Hi-Res range | 1–900 Hz in 1 Hz increments |
| Standard setting increments | 2 Hz below 500 Hz, 5 Hz from 500–999 Hz and 10 Hz above 999 Hz |
| Relay outputs | Two independent volt-free relay outputs |
| Relay contact rating | 5 A resistive at 12/24 VDC |
| Output modes | Normally open, normally closed or pulsing |
| Default Channel 1 settings | High 50 Hz / Low 40 Hz |
| Default Channel 2 settings | High 5,000 Hz / Low 4,000 Hz |
| Protection | IP54-rated case when installed as instructed |
| Overall dimensions | Approximately 68 × 30 × 73 mm |
| Mounting hole centres | Approximately 83 mm |
Terminal Wiring Map
- Terminal 1: Switched +12/24 VDC supply
- Terminal 2: Channel 2 speed input
- Terminal 3: Negative or ground
- Terminal 4: Channel 1 speed input
- Terminals 5 and 7: Channel 1 relay contacts
- Terminals 6 and 8: Channel 2 relay contacts
When only one channel is being used, connect the unused input
channel to ground as specified in the installation instructions.
Typical Conveyor Installation
- Install a suitable magnetic or Hall-effect sensor to monitor the
conveyor pulley, shaft or rotating target. - Connect the sensor signal to Channel 1 or Channel 2.
- Establish the normal conveyor operating frequency.
- Program the required high and low switching points.
- Select normally open, normally closed or pulsing output operation.
- Connect the relay output to the PLC, alarm or external shutdown
circuit. - Test the system under normal running, slowdown and stopped
conditions before placing it into service.
Calculating Conveyor or Shaft Speed Setpoints
The SS501 operates from input frequency in hertz. Where the sensor
produces a known number of pulses per revolution, the frequency can be
calculated using:
Hz = (RPM × pulses per revolution) ÷ 60
For example, a conveyor pulley rotating at 300 RPM with a sensor
producing four pulses per revolution will generate:
(300 × 4) ÷ 60 = 20 Hz
An underspeed or belt-slip threshold can then be set below the normal
operating frequency. The low setpoint should be programmed at least
5% below the high setpoint to provide suitable switching hysteresis
and reduce relay chatter.
The appropriate trip threshold depends on the conveyor design,
sensor location, normal speed variation and required response.
Commission and test all thresholds on the actual equipment.
Popular Conveyor Configurations
- Zero-speed alarm:
Detect a stopped pulley or shaft and activate a warning output. - Underspeed shutdown:
Detect conveyor slowdown or belt slip and interrupt an interlock. - Warning plus shutdown:
Use one speed input with separate relay outputs for two response
levels. - Two-conveyor monitoring:
Monitor two separate conveyors with one SS501. - Crusher and feeder interlock:
Monitor two related machine speeds and create a common control
response.
Important Installation Notes
- Always completely unplug the SS501 before welding on the vehicle
or machine. - Supply the module through a suitable 3 A fuse.
- Install a suppression or flyback diode across external relay and
solenoid coils. - Mount the enclosure with the terminals facing downward to reduce
water ingress. - Do not exceed the maximum input frequency of 9.99 kHz.
- Response time may be longer at very low input frequencies.
- Return the programming switch to RUN before
closing the enclosure.
Need a Conveyor Speed Switch for Your Application?
Contact Bolec Electronics with your conveyor speed, shaft RPM,
sensor type, pulses per revolution and required alarm or shutdown
function. We can help determine whether the SS501 is suitable and
assist with initial setpoint calculations.
