7
7.
Terminating resistor
According to the RS485 specifications, the last device on the bus must be ending with a terminating
resistor 120R. Plug a jumper on the JP2 connector of the last device on the bus to include the 120R
terminating resistor. In the default configuaration the jumper connector is not plugged.
Transmitter functions
The detector's motherboard is equipped by status LEDs, which help in detecting problems during the installation.
LED „POW“ shines at correct power
LED „ALARM“ shines when the alarm level is crossed
LED „ERROR“ shines in case of malfunction or an unstandard situation
1.
Turning on the transmitter
After turning on the power the LED "POW" starts shining and the LED "ERROR" starts flashing, indicating a forming sequence
of the sensor and automatic testing procedures, which can take up to 18 0s depending on the sensor used. The output of the
current loop is 1 mA. During this sequence, testing of internal electronics and stabilization of the sensor in order to eliminate
false alarms after turning on, is taking place. After completion of the formation, a 4 mA current begins to flow on the output of
the current loop and the transmitter starts working according to it's settings.
2.
Gas detection
The transmitter continuously measures the detected gas concentration in the atmoshpere and converts it's current value into
a 4-20 mA signal or transmits it's value to the evaluation unit via DEGA protocol (RS485).
3.
Malfunction
If a malfunction of the electronics or the sensor is found during operation, the transmitter will continue transmitting via
current loop 0,5 mA. On the PCB this condition is indicated by the yellow „ERROR“ LED.
4.
Monitoring the calibration periods
The transmitter continuously checks the calibration validity of the connected sensor.
After 12 months since the last calibration (Max. calibration interval) the LED "ERROR" starts flashing. The connected sensor
must be calibrated immediately. The transmitter will transmit the information about the ending calibration via current loop.
The transmission will be the following: 10 s transmitting a 4-20 mA signal informing about the actual gas concentration
following a 1 second interval of 2 mA current.
Operation, maintenance, inspection and service of the transmitter
1.
Usage limits
To maintain proper operation of the transmitter it is neccesery to respect the fact, that step changes of humidity,
condensation or rapid changes of pressure can cause incorrect indication of the measured value. Each sensing technology is
suited for different methods of application, which is described below. All sensors are characterized by a smaller or larger cross-
sensitivity to other gases than those which are set. Therefore before processing project documentation we recommend to
have the air in the deployment area of the detection system analyzed.
a)
catalytic sensors:
Trace amount of vapors of silicon compounds and sulfur compounds cause a permanent loss of sensitivity,
which requires recalibration or replacement of the sensor. Longterm crossing of the measuring range causes a decrease in
sensitivity. In case of an atmoshpere having an oxygen content of less than 17%, there will be an underestimaton of the
measured value. In case of an atmoshpere having an oxygen content of more than 25%, there will be an overestimation of the
measured value.
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