Additional equipment
Bourdon tube, capsule, diaphragm,
spring diaphragm pressure gauges
37
Electronic contact
The electronic contact with PNP switching output is particularly suit-
able for direct connection to a PLC. Due to the low voltages and cur-
rents, additional switching amplifiers are not required.
Reed contact
Pressure gauges with Reed contact have a bi-stable Reed sensor as
their switching element. The Reed sensor is enclosed in a hermeti-
cally sealed glass tube. The glass tube is covered by a plastic enve-
lope which helps to protect the Reed sensor from damage. The Reed
sensor is a switch which is operated by a magnetic field. The mag-
netic field is generated by a permanent magnet which is attached to
the pointer of the pressure gauge.
Pressure gauges with reed contacts are especially suitable for
switching low voltages in the millivolt or microampere range. Howev-
er, they can also be used for higher switching currents. With voltages
< 5 volts the Reed contact is not subject to mechanical wear.
The switching characteristics of Reed contacts are determined by a
hysteresis which depends on design-specific influences. The hyste-
resis renders the contact insensitive to vibrations and shock and
helps to avoid incorrect switching. In order to obtain high switching
accuracy, this hysteresis needs to be taken into consideration. The
following switching functions are available:
•
Switching on rising pressure (clockwise pointer movement),
normally open contact or normally closed contact
•
Switching on falling pressure (counter-clockwise pointer move-
ment), normally open contact or normally closed contact
Pressure gauges with Reed contact are available with fixed or ad-
justable switching point.
