Switches for Solids Applications
The design of a vibrating level switch for solids must be fundamentally different to the design described for liquids. If two large parallel blades were used on powders or solids it would be too easy for product to build-up and become lodged between the blades causing the oscillations of the switch to stop regardless of product level.
For solids applications on products ranging from cornflakes to coal, it is preferable to have only one blade in contact with the product. This eliminates the potential for bridging between the forks and ensures that the switch does not give false alarms.
The operating principle is the same for all vibrating probe level switches. A piezo-electric crystal is used to force a blade to oscillate at its fundamental frequency (natural resonance). When the blades come into contact with the process medium the natural frequency of oscillation is damped; the electronics sense the change in frequency which causes the unit to switch.
The different electronic outputs to choose from allows the user to switch a load on/off or to interface directly with a computer. The units can be programmed to sense high or low level and failsafe high or low, with adjustable sensitivity to eliminate false switching. The switch is only sensitive at the tip so minimising the effect of build-up on tank walls.
Advantages of Vibrating Probes
- No mechanical moving parts to wear
- No maintenance required
- Simple to install - no adjustments required
- Unaffected by environmental changes
- Unaffected by dust clouds and agitation
- Maximum versatility
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| DP600 Series | 660 Series low cost for OEM | Diamond Point DP120, 130, 140 & 150 |
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Switches for Liquid Applications
TF & MTF Series
As the damping effect (resistance to vibration) of low viscosity liquids is very small, it is common to use two relatively wide blades to sense the presence of liquid levels. These blades can be short in length for minimal intrusion into the vessel or for use in pipes.
The TF Series | |
This rugged design of switch is used throughout the process industries. It is available with a wide range of flanged or screwed process connections and can have extensions, enabling the probe to reach 3 metres into a tank if required. The wetted parts of standard switches are 316 stainless steel but special Halar coated and Hastelloy switches are used for extremely corrosive applications and hygienic probes are available for the food industry. The switch has visual indication of its on/off status and a test point on the side of the housing to allow an operator to check the function of the switch. An intrinsically safe and explosion proof version of the switch is available for hazardous areas. |
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The MTF Series
This is designed specifically for OEM equipment and has a smaller and less expensive configuration, but retains the status LED and test point featured in the TF series.
The MTF Low Cost Series for OEM
Applications for Liquid Switches | |
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