KROHNE VFM 1091 - Manual (Page 26)

Part C Function Checks and Trouble shooting hints
This section describes some functional checks, which can be
performed without using any special equipment. It must be
noted that these checks are very preliminary and do not check
all the functions of the primary head or the signal converter.
To perform preliminary testing of the vortex piezo sensor, the
signal cable of the piezo sensor should be disconnected from
the signal converter electronics. To do this
Always switch-off power source before commencing
work.
l. Use the special wrench to remove cover from
the electronic compartment. Ensure that screw
threads of electronic compartment cover are
well greased at all times.
2. Remove screws A and turn display board to one side.
3. Remove the piezo cable from the preamplifier board at
location Z by its (and not by pulling cable itself!)
4. Do the following tests on the sensor cable
Capacitance between centre pin and each outer pin
Resistance between center pin and each outer pin
>200M ohm. Also resistance between each sensor
7. Functional checks
wire pin and earth should be >200 M ohm. Also short out
all three pins & measure resistance between these pins &
Earth. This should be > 200 M W
5. Reassemble converter.
7. 1 Primary head functional checks
7. 2 Signal converter functional checks
7.2 Vortex Sensor
7. 2 .1 Self diagnostics
On power-on VFC 091 carries out diagnostic
checks wherein the instrument checks its functional elements
as
far as possible. Diagnostic failure result
in fatal errors and are indication of a hardware fault
within electronics. Usually it is necessary to replace
electronics in such cases.
7. 2 .2 Display check
Display functionality can be checked by the use of
Fct 2.1 TESTDISP.
This function flashes all the segments of the display.
Preamplifier
flat cable from
CPU to Preamp
board
A
Power
supply
board
D
D
Z
A
Flat
cable to
display
board
CPU board
7. 2 .3 Current output check
Fct.2.2 TEST I can be used to test current output function of
VFC 091. With this function it is possible to generate
following
test values- between 4 and 20mA
(integer values only)
Current output electronics is factory calibrated and
should be within +/- 0.02mA. Otherwise re-calibration of
current output is necessary by KHRONE MARSHALL
service person.
7. 2 .4 Pulse output check
Fct. 2.2 TEST P is meant for checking the pulse output
function with a power supply (24VDC) connected through a
load of lk/1W to pulse output terminals 4.1 & 4.2, and the
output level (high or low) monitored with a voltmeter.
7. 2 .5 Frequency measurement check
Disconnect the sensor cable from the electronics as indicated
in section 7.1.1 and feed a signal (sine or square wave) to the
sensor connector Z on the preamplifier board. The signal
should be fed between the center pin and one of the outer pins
of the connector Z. The value of frequency fed should be
indicated on the display when frequency measurement is
enabled. This can also be checked with the help of the VS1 or
VS2 Vortex Simulator in place of the signal source. The
amplitude of the signal l should be 50mVp-p and the
frequency between 2Hz and a value
equal to Qmax (m/hr) x K-factor (Pulses/m) max
3600
26