Instructions for Use
– SCHMIDT
®
Flow Sensor SS 20.500
Page 32
Error image
Possible causes
Troubleshooting
Problems with supply U
B
:
No U
B
available
Wrong polarity of
DC-supply
U
B
< 15 V
Sensor is defective
Plug-in connector screwed
on correctly?
Supply voltage connected?
Voltage at sensor plug
available (cable break)?
Power supply large
enough?
No LED is shining
Both signal outputs at zero
Start sequence is repeated
continuously (all LEDs
flashes simultaneously red
- yellow - green)
U
B
unstable:
Power cannot supply
switch-on current
Other consumers over-
load power source
Cable resistance too
high
Supply voltage at sensor
stable?
Power of supply unit
sufficiently?
Voltage losses over cable
negligible?
Sensor element defective
Send in sensor for repair
Electronic temperature too
low
Increase temperature of
environment
Electronic temperature too
high
Decrease temperature of
environment
Medium temperature too
low
Increase medium
temperature
Medium temperature too
high
Reduce medium
temperature
Flow signal w
N
is too large /
small
Measuring range too small
/ large
I-mode instead of U-mode
Measuring medium does
not correspond to air
Sensor head is soiled
Check sensor configuration
Check measuring resistance
Gas correction considered?
Clean sensor tip
Flow signal w
N
is fluctuat-
ing
U
B
unstable
Sensor tip is not in opti-
mum position
Let-in or let-out distance is
too short
Strong fluctuations of pres-
sure or temperature
Check voltage supply
Check installation conditions
Check operating parameters
Analog signal in U-mode
has offset or is noisy
Measuring resistance of
signal output is at GND
Connect measuring
resistance to AGND
Analog signal permanently
at max.
Measuring resistance of
signal output is at U
B
(DC)
Connect measuring
resistance to AGND
Analog signal switches be-
tween min. and max.
Measuring resistance of
signal output is at GND
AC
Connect measuring
resistance to AGND
Table 9
