7
Service
and Maintenance
71
7.2
Checking the LT 2/KS1-DK
7.2.1 Checking the measurement input of the LT2/KS1-D
Connect a digital voltmeter to terminals 33 (-) and 34 (+) parallel to the probe.
Compare the measured O
2
voltage with the displayed probe voltage (U-O2).
Range: -20 mV … +300 mV.
If the deviation is less than 1 mV, the LT2/KS1-D is in good working order.
If the deviation is greater than 1 mV, repeat the measurement with another digital
voltmeter.
Connect a digital voltmeter to terminals 12 (-) and 34 (+) parallel to the probe.
Compare the measured CO/H2 voltage with the displayed CO/H2 voltage ( U-CO/H2).
Range: -50 mV … +950 mV.
If the deviation is less than 10 mV, the LT2/KS1-D and the buffer amplifier are in good
working order.
If the deviation is greater than 10 mV, repeat the measurement with another digital
voltmeter.
CAUTION:
Check the measurement accuracy of the connected digital voltmeter.
If there is still a deviation
→
check the buffer amplifier or replace the device.
Measuring range of buffer amplifier: Input -50...+950mV, output 0...20mA
From January 2007, the buffer amplifier is no longer installed and is replaced by a
special input card. Measuring range -200...+1000mV.
7.2.2 Checking the probe: internal resistance measurement Ri probe
Only possible with probe simulator LS 2 Order No. 655 R 1030.
Connect the probe simulator to terminals 33 (-) and 34 (+).
With the R
I
probe potentiometer, set an internal resistance of < 200
Ω
.
Check using the voltmeter as follows:
Measure the alternating voltage between terminals 33 (-) and 34 (+).
The display in mV roughly corresponds to half the probe internal resistance.
If R
I
- >200 , a warning “LS 2 internal resistance too high” is displayed after 10
seconds, if R
I
> 300
Ω
, a fault
”Probe broken wire/faulty probe”
appears
Example: 75 mV = 150
Ω
NOTE:
Probe internal resistance monitoring is deactivated during “cold start”.