KROHNE CORIMASS G-MFM 4085 EN - Manual (Page 91)

91
8.8 Checking the Primary Head
Remember! Always switch the power off before opening the converter housing.
Required tools and test equipment
– Phillips screwdriver
– Multimeter
– Special wrench to unscrew converter housing lids
8.8.1 Compact Meter
A. Screws that hold the display
PCB in place.
B. Ribbon cable connecting display
PCB to converter electronics.
C. 10-pin sensor connector.
D. Screws that hold the converter
electronics in place.
P. Power supply circuit board
Preliminary preparation
– Remove front lid of electronic housing
– Unscrew the two screws ”A” that hold down the display PCB and fold the ribbon cable and
PCB carefully to one side.
– Unplug blue primary connector ”C” from amplifier board
10-Pin Sensor Connector ”C” (Connector between primary and converter)
(g
re
y)
(w
h
it
e
)
(b
lue)
(g
reen)
(v
io
le
t)
(b
la
ck
)
(b
ro
w
n
)
(o
range)
(y
e
llo
w
)
(r
ed)
Colours in parenthesis are valid for Ex-converters
Testing the resistance values of
the sensors and exciter Typical values Assessment of
measured values
1 Measuring tube driver:
Measure between grey and black
30 - 50 ohm
2 To check sensor A and B:
Measure between:
green and violet (Sensor A)
white and yellow (Sensor B)
50 - 130 ohm
Measurements outside
typical values:
Primary faulty
Replace or call Krohne
service.
3 To check the temperature
sensor (RTD):
Measure between blue and red. 500 - 550 ohm
(ambient temperature
dependent)
Measurements inside
typical values:
Sensor OK
4 To check the strain gauge:
Measure between orange and red.
400 - 600 ohm
C
P