Additional equipment
36
Bourdon tube, capsule, diaphragm, spring diaphragm pressure gauges
Magnetic spring contact
The design of magnetic snap action contacts is similar to that of slid-
ing contacts. This type of contact features additional magnets to ac-
celerate the contact action.
To close the circuit, the contact pin of the moving contact arm is at-
tracted by the magnet so that the contact snaps closed. When the
circuit opens, the magnet attracts the contact arm until the resetting
force of the measuring element overcomes the effective force of the
magnet so that the contact snaps open.
The snap action reduces arcing between the contacts, thus allowing
for greater switch ratings. Due to the increased contact force, this
type of contact is also less sensitive to vibrations and achieves a
high switching reliability.
Magnetic spring contacts can be used under almost any type of op-
erating condition. They can also be integrated into liquid filled pres-
sure gauges. In order to help prevent switching errors (particularly in
the case of greater inductive switch ratings or considerable system
vibration or in gauges with filling), it is recommended to install the
pulse-controlled series MSR contact protection relays.
Information on the nominal operating voltage, the nominal current,
the switch rating and the switching function are shown on the dial or
the nameplate.
Standards: EN 60947-1, EN 60947-1A11, EN 60947-5-1.
Inductive contact
Inductive contacts have non-contacting electric displacement pick-
ups as per DIN 19234.
Inductive contacts are used together with an isolating switching am-
plifier. The switching amplifier supplies the control head with direct
voltage. As soon as the control flag reaches the control head, the in-
ternal resistance in the control head increases. This causes the cur-
rent to change which is used to control the switching amplifier. The
amplifier converts the input signal into a binary output signal.
Due to non-contact switching, the high switching accuracy and the
long service life, inductive contacts are suitable for industrial applica-
tions and should be used in liquid filled pressure gauges.
If suitable isolating switching amplifiers (such as WE77/Ex) are used,
the system will have the type of protection intrinsic safety "i". It is
classified as EEx ib IIC T6 and approved for use in hazardous areas,
zones 1 and 2. Stainless steel pressure gauges for chemical applica-
tions are approved for use in hazardous areas, zones 1 and 2.
The isolation switching amplifier must always be installed outside of
the hazardous area.
