Level Switches and Probes: How to Choose Between Vibrating, Thermal Dispersion and Float
Point level detection is essential for pump protection, overflow prevention and control of tank and hopper loading/unloading. Choosing the technology depends on the material (liquid or solid), temperature, pressure, presence of solids, foam or adhesion, and classified area.
1. Vibrating switch (tuning fork)
The vibrating level switch uses a prong or tuning fork vibrating at a natural frequency. When the material contacts and dampens the vibration, the instrument detects the change and switches its output.
- Advantages: Very versatile (works in liquids and dry solids), insensitive to conductivity, density, foam and turbulence; robust; suitable for pump protection.
- Limitations: Can be affected by very viscous materials that adhere and permanently dampen the vibration, causing false alarms.
- Applications: High/low alarms in liquids, fine/powder level detection in solids, pump and mixer protection.
2. Thermal dispersion switch
The thermal dispersion switch is based on heat dissipation: one sensor is heated and the other measures the reference temperature. In the presence of liquid (which conducts heat faster than gas), the temperature difference between both sensors changes sharply.
- Advantages: Detects the turbulence point in flow and level; suitable for gases and liquids; insensitive to foam, vapors and conductivity; no moving parts; useful for flow detection in lines.
- Limitations: Less suitable in materials with very low thermal conductivity; requires stable contact of the media with the sensor.
- Applications: Flow detection in pipes (pump protection), point level in liquids and gases, seals, gas/liquid interface indication.
3. Float or paddle switch
The float switch uses a float that moves with the level and actuates a microswitch or reed switch. It is the simplest and most economical technology.
- Advantages: Low cost, simple, does not require external power on its own (depending on design), reliable in clean liquids.
- Limitations: Moving parts subject to wear, jamming or adhesion; sensitive to agitation, turbulence and solid accumulation; not suitable for very viscous or dirty fluids.
- Applications: Water tanks, condensate, lubricants, simple high/low applications in clean liquids.
4. Conductive switch
The conductive switch measures electrical conductivity between two electrodes when the conductive liquid establishes contact between them.
- Advantages: Economical, robust, no moving parts, suitable for conductive aqueous liquids and for multiple points with several electrodes on a single rod.
- Limitations: Only works with conductive liquids; electrodes may scale; not suitable for dry solids.
- Applications: Water, wastewater, aqueous solutions, pump protection in conductive liquids.
5. Selection criteria
| Criteria | Vibrating | Thermal | Float | Conductive |
|---|---|---|---|---|
| Dry solids | Yes | No | No | No |
| Liquids | Yes | Yes | Yes | Conductive |
| Moving parts | No | No | Yes | No |
| Sensitive to foam | No | No | Yes | Partial |
| Relative cost | Medium/high | Medium | Low | Low |
Conclusion
For maximum versatility in liquids and solids with robustness, the vibrating switch is the most recommended option. For flow and turbulence detection, thermal dispersion is ideal. Float and conductive switches are economical solutions for clean and conductive liquids, respectively. The decision must consider the material, pressure, temperature and classified area.
MARPATECH SAC represents in Peru, Argentina and Colombia high-performance level switches from SOR, including vibrating and thermal dispersion technologies, with classified area certifications and field technical support.
Frequently asked questions
Yes, vibrating switches work very well in dry and bulk solids, such as powders, grains and aggregates. They detect the dampening of vibration when the material touches the prong.
The vibrating switch is the most robust option for dry-run pump protection, as it reliably detects the absence of liquid and is insensitive to foam and turbulence. Thermal dispersion also works when flow detection in the line is also desired.
Turbulence can cause false signals in float switches. Vibrating and thermal dispersion switches tolerate turbulence better; if severe, a stilling well can be installed or the sensor located in a lower agitation zone.