Ex PC-Workstations, Ex-PCs
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Digital solenoid valve technique While purging, the SVD is activated and a big amount of purge medium flows inside the enclosure through a nozzle with a large cross-section. After purging, the control unit turns off the SVD. The leakage compensation is made by a bypass choke, with a very small adjustable cross-section (diameter 0.3 ...1 mm) inside the valve. The protective medium that flows into the enclosure now is adequate to maintain a pressure of at least 0.8 mbar. The pressure is monitored by the control unit FS850S. The maximum and minimum pressure of the enclosure is programmable. Purging period For purging, a common and a new integrating method is available:
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figure 1: consumption of protective gas |
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The digital solenoid valve technique has a considerable disadvantage: while purging process and normal operation, a constant rate of protective gas is needed. Of cause of safety the rate must be bigger than leakage rate of the enclosure. But wasting protective gas causes high costs in many applications. Proportional solenoid valve technique sing proportional solenoid valve technique stops wasting protective gas. The internal proportional working sensory equipment and a proportional valve as actuator are combined to a pressure feedback control system. Advantages of pressure feedback control are:
pressure feedback control while purging Another advantage using a proportional solenoid valve is; that pressure control is used even during purging. A set-point pressure will be achieved in the enclosure, while the flow volume, that leaves the enclosure, will be recorded and integrated through time, until the required purge volume is achieved. Advantages of this method are:
Operation mode continuous flow The control unit FS850S has moreover the operation mode "continuous flow" implemented. This operation mode is necessary, for example, if an analyzer could produce an explosive atmosphere inside the enclosure (containment system). The operation mode continuous flow purges the enclosure permanently. After the (pre-)purging procedure (purging process) a set-point flow rate is adjusted during normal operation. The monitored flow rate minimum is adjustable. The operation mode continuous flow can be realized using 2 digital solenoid valves as well as using one proportional solenoid valve.
For the control unit FS850S several operating and visualizing panels are available. The panels have the explosion protection class intrinsically safe and are very advantageous, particularly when the control unit is mounted inside the enclosure. |
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Bedientableau BT851.1 |
1. Common operating panels: BT 814.1 and BT 815.1 with
2. Intelligent operating panel type BT 851 |
This operation panel indicates operation and malfunction reports as text messages. Using the 4 membrane switches offers total command of the control unit. Status, momentary pressure and flow rate as well as remaining purge time are always available. Option Pressure loss alarm This option means an addition pressure monitoring on a programmable level. the alarm is indicated on terminal 21/22 on the FS850S. If the pressure falls spontaneously below the level the EEx e relay on te 21/22 opens. |
last modified: 09.04.2020 |