When coal, cement, grain or ore piles up where it should not, a simple hanging probe can stop a conveyor before the spill becomes a shutdown. This guide explains how that probe works and how to install it so it trips every time.
A tilt switch is one of the cheapest and toughest point level devices for bulk solids. Learn its working principle, trip angle, mounting styles, wiring, testing and the six places it earns its keep.
What Is a Tilt Switch?
A tilt switch is a point level device that hangs or projects into a bin, chute or pile and changes its contact when rising bulk material pushes it away from vertical. It is a member of the wider family of level switches, built especially for rough, dusty solids handling.
Inside the housing sits a gravity sensitive element, either a mercury capsule in older designs or a ball, pendulum or snap action mechanism in modern mercury free designs. When the housing leans past its trip angle, the element moves and opens or closes a contact.
Because it needs no power to sense, the device is just a rugged contact, similar in spirit to a limit switch. It does not care about dust, dielectric constant or material moisture, which troubles many other sensors.
How the Probe Senses Rising Material
Monitor Technologies specifies an actuation angle of 17 degrees from vertical for its TC series, in any direction across a full 360 degree arc. BinMaster quotes about 15 degrees for its tilt models, so most products trip somewhere in that band.
The probe resets when material falls away and it swings back to vertical. Older units used a mercury bulb like a reed switch capsule, while new units use a steel ball or weighted pendulum acting on a microswitch or a magnet and sensor.
The Monitor Technologies TC 1 and TC 3 need no external power at all. The tilting mechanism directly operates an SPDT contact rated up to 15 A or 10 A at 250 V AC.
6 Practical Tilt Switch Uses in Bulk Handling
Leveltec notes that its probes monitor blocked chutes, stockpiles and conveyor transfer points so that the control system can stop equipment before spills and downtime. In a cement or thermal power plant, those spots sit next to conveyor safety switches such as pull cord and belt sway switches.
For true continuous inventory in a silo, a point probe is not enough, and engineers add radar or weighing. The overview in how to select the right level sensor compares those choices.
Tilt Switch Types and Mounting Styles
Hangs on a chain or wire rope and swings freely when material pushes it.
Fixed housing with a shaft and paddle or sphere that the material deflects.
Ball or pendulum operates a sealed microswitch, no mercury inside.
Older design using a mercury bulb as the contact.
BinMaster offers stationary tilt units with probe shafts from 1 to 8 feet, a standard 1¼ inch process connection, and mounting plates at 0, 10 or 30 degrees. It also states a minimum bulk density of 15 lb per cubic foot, about 240 kg per cubic metre, for reliable actuation.
Very light, fluffy powders may simply flow around the probe without tipping it. For those, a rotary paddle switch or a vibrating fork switch is usually the better choice.
Fit the probe with a sphere or paddle extension on light materials. The larger contact area turns a gentle push into enough torque to reach the trip angle.
Tilt Switch Trip Geometry Formula
For a cable suspended probe, the swing needed to trip depends on the distance from the hanging pivot to the switch body and on the trip angle. Knowing this distance tells you how far the pile must push the probe sideways and how much it lifts.
Vertical rise h = L × (1 minus cos θ)
L = pivot to probe centre, m
θ = trip angle from vertical
Example:
L = 1.2 m, θ = 17 degrees
sin 17° = 0.2924, cos 17° = 0.9563
x = 1.2 × 0.2924 = 0.351 m
x = 351 mm, h = 1.2 × 0.0437 = 52 mm
Tilt Switch Swing Calculator
A long hanger means the material must travel a long way sideways before the alarm, so the real alarm level sits lower than the probe tip. Keep the hanger short when the alarm must be sharp.
Second Worked Example: Chute Plug Response
Suppose a short hanger of 0.4 m holds the probe in a transfer chute and the trip angle is 15 degrees. The swing is 0.4 × sin 15° = 0.4 × 0.2588 = 0.104 m, so about 104 mm of sideways push is enough.
If the chute receives 300 tonnes per hour, it fills fast once it plugs, so add only a short time delay of 1 to 3 seconds in the PLC timer to ignore surges. Then trip the upstream feeder, as in a first out alarm sequence that records which device stopped the line.
The Minamata Convention on Mercury lists switches and relays among the mercury added products that member countries agreed to phase out. That is why most new bulk handling projects specify mercury free units.
Installing a Cable Suspended Tilt Switch
The Monitor Technologies manual is clear that the switch must never be hung by its electrical cable and asks for SO or STO rated extra hard usage cable. It specifies a cord diameter of 6.4 to 9.6 mm for a proper seal at the gland.
The TC series is rated NEMA 4 and IP56, so check the IP rating against washdown and dust levels at site. In coal, sugar or grain dust areas, also check the hazardous area zone for combustible dust.
Hang the probe out of the main falling stream of material. A direct hit from a lump of ore or coal can swing it and cause false trips, or damage the housing.
Wiring the Tilt Switch to the PLC
Most units offer a dry SPDT contact, so wire the normally closed side as a fail safe signal that opens on alarm or on a broken wire. Feed it from the PLC 24 V DC supply, and follow the sinking and sourcing convention of the input card.
When the contact must switch a motor contactor or hooter directly, check its AC rating and add an interposing relay with coil suppression for inductive loads. This protects the contact and gives a clean signal.
Tilt Switch vs Other Bulk Solids Level Switches
| Feature | Tilt Switch | Rotary Paddle | Vibrating Fork | Capacitance |
|---|---|---|---|---|
| Power to sense | None | Motor | Electronics | Electronics |
| Light powders | Poor | Good | Good | Good |
| Heavy lumps | Excellent | Fair | Fair | Good |
| Chutes and piles | Excellent | Poor | Poor | Fair |
| Relative cost | Low | Medium | Medium | Medium |
A capacitance level switch suits sticky or fine products in a bin wall, while the hanging probe wins in open piles and chutes where nothing can be wall mounted.
- Simple, rugged and low cost.
- Needs no power to sense.
- Unaffected by dust, moisture or dielectric constant.
- Ideal for chutes, stockpiles and conveyors.
- Needs enough bulk density to tip the probe.
- Single point signal only.
- Falling material can cause false trips.
- Hanger wear needs periodic checks.
Testing and Troubleshooting Tilt Switch Faults
- Push the probe past its trip angle in each direction.
- Confirm the PLC input changes and the alarm appears.
- Check the hanger chain, eyebolt and shackle for wear.
- Inspect the cable loop for cuts and strain.
- Check the gland seal and housing for dust ingress.
- Verify the time delay setting in the PLC.
- Record the test in the maintenance log.
If the alarm never comes, check whether the probe is caught on a structure or buried under a crust that keeps it vertical. If it chatters, look for material falling onto it or a hanger that lets it swing in air flow.
A useful habit is to include the tilt switch in the same monthly round as other bulk handling devices, and to revisit the basics of level measurement when alarms start to disagree with the real pile.
Monitor Technologies Tilt Switch Manual
BinMaster Tilt Switch Video
Tilt Switch FAQ
It is used as a point level alarm for bulk solids such as coal, cement, ore and grain. It signals high level in bins, plugged chutes, conveyor overload and stockpile height.
The probe hangs or projects into the space where material builds up. When the pile pushes it past its trip angle, an internal contact changes state and alerts the control system.
Monitor Technologies specifies 17 degrees from vertical for its TC series, in any direction around a full circle. BinMaster quotes about 15 degrees for its own range of probes.
The exact value depends on the internal mechanism of each product. Check the datasheet, because the hanger length and this angle together set the true alarm level.
Mercury is toxic, and broken capsules create a hazard in food, pharma and general plants. The Minamata Convention also lists switches among the mercury products to be phased out.
Modern ball, pendulum and snap action mechanisms give the same simple operation without mercury. Most new project specifications in India and abroad now ask for them by default.
It works poorly with very light or fluffy powders that flow around the probe without tipping it. BinMaster states a minimum bulk density of about 15 lb per cubic foot for reliable operation.
Adding a sphere or paddle extension increases the push on the probe. For very light products, a rotary paddle or vibrating fork switch is usually a better choice.
Hang it from a chain or wire rope fixed to the eyebolt of the housing. Never support the weight of the probe with its electrical cable, because the gland and conductors are not designed for that load.
Leave a loose cable loop so the probe can swing freely in every direction. Keep it clear of walls and out of the main falling stream of material.
Most models give a dry SPDT contact that needs no power for sensing. Wire the normally closed side so the signal opens on alarm and on a broken wire.
Add a short time delay in the PLC program to ignore brief surges of material. Use an interposing relay if the contact must switch an inductive AC load directly.
Push the probe past its trip angle by hand in several directions with the plant safely isolated. Confirm that the PLC input changes and that the correct alarm appears on the screen.
Inspect the hanger, eyebolt, cable loop and gland at the same visit. Record the result in the maintenance log so the next round has a reference.
Related Articles
- Paddle Type Level Switch
- Vibrating Fork Level Switch Working
- Conveyor Safety Switches Types
- Capacitance Level Switch Working
- Level Switch Selection Guide
External References
- Tilt Switch Level Monitors TC 1 and TC 3 Manual, Monitor Technologies
- Tilt Switch Level Sensors, BinMaster
- Level Sensor, Wikipedia
What We Learn Today
- A tilt switch trips when bulk material pushes the probe about 15 to 17 degrees from vertical, changing an SPDT contact without any power for sensing.
- It is ideal for plugged chutes, conveyor overload, stockpiles and bin high level, but needs enough bulk density to tip the probe.
- Horizontal swing at trip equals hanger length times sin θ, so a 1.2 m hanger at 17 degrees needs about 351 mm of push.