Technical data

Greater safety

· in process engineering and chemical installations,
· in gas and liquid gas installations

Basic features:

– “Of special construction” according to VdTÜV Memorandum “Pressure 100”
– Line break and short circuit monitoring-between pressure switch and isolating amplifier
– Suitable for Ex-areas (zone 0, 1 & 2 or 20, 21 & 22) (explosion protection Ex-i)
– Protection class IP 65
– Plastic-coated housing (chemical version)

Options:
– Limiter with internal interlock

Type specific features:

– Self-monitoring sensors
– Positive opening microswitches
– Gold plated contacts
– TÜV, DVGW component tests

Safety requirements for pressure limiters
Pressure limiters “of special construction” (DBS) must fulfil additional safety requirements, i.e. breakage or leakage in the mechanical part of the sensor must lead to shutdown to the safe side. The pressure limiter must respond as if the system pressure had already exceeded the maximum limit. The control circuit for the pressure limiter must also be considered from the point of view of safety, as short circuits in the supply lines or other faults in the control current circuit can lead to dangerous conditions.
Switching element with positive opening operation and gold plated contacts
The microswitch is equipped with positive opening operation. Rather than transmitting the plunger force via a spring, which is the usual method with most microswitches, this newly developed microswitch has an additional lever which transmits the movements of the pressure bellows positively to the contact lever. If the spring breaks, the contact lever is moved directly.
Line break and short circuit monitoring in the control circuit
The resistor connected in series with the switching contact limits the current to a defined value with the switch closed. In the event of short circuit in the area between the isolating amplifier and the series resistor, the current rises above the predetermined limit value, the relay of the isolating amplifier drops out, the output current circuit is interrupted and thus the safe condition is achieved. In the event of a line break, the current flow is interrupted, the relay drops to the safe side and interrupts the output current circuit (safety sequence). Furthermore, the isolating amplifier is designed so that, if faults occur in the electronics (conductor interruption, component defect etc.) and in the resulting situations, the safe shutdown condition is assured. These characteristics of the safety engineered isolating amplifier, including line break and short circuit monitoring, satisfy the requirements of DIN/VDE 0660, Part 209.
Connection diagram
For pressure monitoring in Ex-areas, the isolating amplifier must be installed outside the Ex-zone.
The pressure limiter has an intrinsically safe control current circuit (Ex-i). This arrangement is suitable
for zones 0, 1 and 2, 20, 21 and 22.