VEGA D77 Hydrostatic pressure transmitters - Manual (Page 20)

20 Pressure transmitters D76 and D77
Diagnostics
6 Diagnostics
6.1 Maintenance
Pressure transmitters D76 and D77 are main-
tenance-free.
6.2 Failure rectification
Due to continuous self-monitoring, series D70
pressure transmitters offer maximum reliabil-
ity. However, should failures occur, check the
following before removing the pressure
transmitter:
- the atmospheric pressure compensation,
- the electrical connections.
Checking atmospheric pressure com-
pensation
First open the cover of the housing, in which
the atmospheric breather facility is located.
The displayed measured value must not
change. However, if the displayed value
changes, compensation of the atmospheric
pressure is not ensured, which will lead to
distortion of the measured value. Therefore
check:
- the breather facility on the housing
- VEGADIS 12 or VEGABOX 01
- the capillary tubes in the special cable.
Note:
There must always be the same atmospheric
pressure on the breather facility as in the
open vessel.
Voltage
- the terminal voltage on the pressure trans-
mitters must be at least 12 V DC
Current
Current value Condition
3.8 … 20.5 mA standard range for the output
current
0 mA signal cable interrupted
< 3.6 mA sensor electronics or pressure
sensor element defective
22 mA sensor electronics or pressure
sensor element defective
Note for Ex applications
Deviating from above regulation, here termi-
nals 1 and 3 (on VEGADIS 12 terminals 10
and 12) are used only for brief connection to
a certified active, floating measuring instru-
ment (max. value: 470 mW) or an individual
passive, floating ammeter. When connecting,
the regulations for wiring of intrinsically safe
circuits (measuring instrument, supply and
signal circuit) have to be observed.
Checking electrical connections
Pressure transmitter
terminals
~
1 2 3
+
-
Voltage Current
Current
External
energy source
V mA
mA