High level alarm switch on bitumen loading systems

The VegaSwing tuning fork is a highly effective solution: a stainless steel cage protects the sensor, which is cleaned by plunging into a solvent to avoid build-up after each loading operation

On a bitumen filling station, the process of charging into road tankers needs to be totally secure to guarantee a safe transfer of the bitumen.

This is a critical process as the product is maintained at very high temperatures and is very adhesive if splashed or spilt.

A high security level switch is needed for overfill protection and to protect the surrounding staff against burns.

Alternatives don't always fail 'safe': float devices may be coated or damaged, back pressure systems can get leaks, and capacitive devices can be incorrectly adjusted.

The use of a tuning fork level switch is a highly effective solution.

Elements such as pressure, temperature, foam, bubbles and product viscosity do not influence the precision of switching.

To protect the tuning fork during the loading operation, it is surrounded with a stainless steel cage.

Furthermore, these detectors are continuously fault monitored.

A four function test to check the the linked system (pump, alarms etc) can be initiated with a remote test button.

After loading, the head of the arm is plunged into a receptacle loaded with solvent to avoid build-up by hardening of the bitumen on the whole filling mechanism, this also stops the hardening happening on the switch.

A tuning fork level switch is energised by a piezo crystal and vibrates at its resonant frequency of approximately 380Hz.

A second crystal detects this frequency, which is then passed to the integral electronics.

If the VegaSwing tuning fork is covered by liquid, the resonant frequency is reduced, this change is detected by the integral electronics and converted into a switch signal.

If there is significant build up or damage to the switch, the switch will always 'fail safe', as the fork element always needs to vibrate freely and at the correct frequency to be ready to detect liquid presence.

Benefits:.

* Maximum safety: fail safe and reliable overfill security to SIL 2/WHG.

* Temperatures up to 250C.

* Simple to implement and simple to test.

* Robust, modular design.

* ATEX Approval.

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