8 / 32
IS DT300 200928
Eng
li
s
h
DT300
Altering the alarm thresholds
After connecting the instrument, the three actual thresholds of C, B & A alarms are visualized on the bottom row
of digits. Adjust at the corresponding potentiometer, to reach desired value. See Fig. 7.
In the datasheet of the actual sensor head, the desired alarm levels can be read as PPM / % values and as a
corresponding voltage value VDC. In order to check the corresponding PPM / % value for a threshold value in
VDC, one starts by finding the VDC value at the vertical axel. Then following an imagined horizontal line until it
reaches the graph, and thereafter following an imagined vertical line until it reaches the horizontal axel of the
diagram.
On the horizontal axis the corresponding PPM / % value can be read. If one likes to find the corresponding
VDC-value for a certain PPM / % value, the procedure is to be carried out in the opposite order (See example
sensor graph, Fig. 10).
Alarm thresholds should be chosen within the area of the solid line of the graph. If
values are chosen from the area of the dotted line, there are significant risks of
distortion with false alarms or total absence of alarm consequently.
11. Check of the response-
and recovery time of the sensor by performing a “bump test”
After check and eventual adjustments of the sensor off-set, a function control is to be carried out. By exposing
the sensor to a small amount of concentrated gas directly to the sensor head, the response- and recovery time
can be checked. The sensor head shall be exposed, and eventual splash protection removed during the test.
The comprehension is that the sensor signal is within the “normal” area when exposed to clean air (the green
area of the sensor graph)
- Expose the sensor to the actual gas for 5 sec maximum, the sensor should react instantly and reach > 4VDC
within 2-5 sec.
- The signal output should reach the start level within ~ 5 minutes after finished gas exposure. (see quick
response- and recovery time for a healthy sensor, Fig. 11)
Most SC-sensors can be checked with Butane gas, as used in ordinary cigarette lighters.
If the response- and recovery time is slow, or if the output signal does not reach the start value according to the
suggested time frame, the sensor is probably contaminated and shall be replaced.
Fig. 12 shows a slow response- and recovery time of a contaminated sensor.
12.
Battery indication ”low Batt”
The LED “Low Batt” will light up with a constant light when the batteries are close to empty. When the LED
starts to flash, the batteries are to be replaced.
13. Troubleshooting
If the actual detector does not generate an alarm when exposed to gas. Check the following:
- GV-offset and sensor signal due to point 6 and 8
- Alarm threshold settings
- DIP-switches, settings of alarm delay
- That the detector is not in the service mode
Storage of the instrument
It is of significant importance to the reliability of the instrument,
that the storage conditions are such, that it is not exposed to substances that can
contaminate or damaged the sensor head of the instrument.
This product is intended for use in the industrial area.
Technical specifications are subject to change
