Nitric oxide sensors are sensitive to water vapor and condensate. Immediately after starting the engine, the risk of water hammer is highest. The ceramic sensor tip is heated to 800° C operating temperature. If a drop of water hits it, it shatters immediately. For this reason, the probe preheats the tip to 80° C after powering up. The transmitter now waits 5 minutes until the motor has reachd normal operation conditions and then sends a signal to the probe. This then heats up in several stages up to the operating temperature and starts measuring the nitrogen oxide content in the exhaust gas.
The probes have a communication interface with CAN bus. A CAN bus signal can be transmitted over distances of up to 15 metres. This is often not sufficient for combined heat and power units (CHP), stationary engines and ship drives. Therefore, the transmitter converts the measured ppm signal into a 4-20 mA signal, which is independent of the line length. This current signal can be processed by any downstream PLC control system. Thus, existing plants can be retrofitted with SCR systems (Selective Catalytic Reduction). The system consists of a 24V nitrogen oxide probe with a measuring range of 0-1500 ppm, a cable connection between probe and transmitter as well as the transmitter and will be offered by EngineSens from October 2018. The transmitter is suitable for DIN rail mounting and indicates the respective operating status via status LED.
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