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DDP involves the transmission of a beam of light across the stack, from a transmitter to a receiver, much like a traditional opacity monitor. However, instead of measuring the attenuation of the overall light strength (the DC component), we monitor the amplitude of the ripple on-top of that signal (the AC component). The ripple is introduced as interference to the light beam by the passing particulate in the stack, and the amplitude of the AC component is directly proportional to the volume of particulate passing through the light. Furthermore, as the DC light signal decreases (with the deposition of fixed particles on the external surfaces of the lenses), the variations in the AC component remain unaffected. This means that DDP can remain unaffected by dirty optics right up to the point at which there is not enough signal to make any measurement at all, where as traditional opacity monitors would have drifted all the way.
The DSL-6000 is designed to measure volumetric density (mg/m³) as its primary unit of measure and therefore requires in-situ calibration to EPA Method 5/17 or European standard EN13284-1.
The DSL-6000 also has an on-board automatic zero and span verification feature. This feature uses electronic control of the transmitted light beam to verify drift in the zero and span settings, thus confirming the consistency of the calibration. Use of the DDP technology means that any drift observed should be negligible, but this feature is sometimes required regulatory authorities to meet the specification laid down by traditional opacity monitors.
The instrument consists of a pair of sensors (a transmitter and receiver) mounted on the stack using standard flange fittings, and an operator interface (a control unit) fitted up to 1km away, either at the base of the stack or in a control room.
All signal processing is performed in the sensors using the latest generation microprocessor electronics. Data is exported from the sensors via serial link (RS485) to the operator interface which has a human interface is the form of a display/keypad, and an electronic interface in the form of relay contacts, analogue outputs, and serial comms (RS232/485). Furthermore the operator interface offers the facility to add plug-in interface modules enabling comms with a variety of generic bus systems, such as ModBus, Profibus, DeviceNet, Ethernet etc.
The sensors are of rugged construction with a high environmental rating. Both heads are supplied with stainless steel air purge bodies, which when connected to an airline will serve to protect the optical surfaces from dirt and particulate deposition – prolonging service intervals. The sensors themselves are attached to the back of the air purge bodies with quick release catches, affording speedy access to the lenses for ease of maintenance.
The operator interface is housed in a rugged weatherproof enclosure designed for wall mounting. The human interface consists of a clear single line VFD display (visible in completely dark conditions as well as sunlit environments) and a 20 key numeric keypad. The wiring terminations are made to two part terminal blocks inside a terminal compartment dedicated access.
Note: The DSL-6000 operator interface is now available in a 4U 19” rack enclosure, for easy integration into CEMS packages – quote DSL-6000R.
The DSL-6000 and DSL-6000R represent the perfect solution to your high accuracy particulate monitoring requirement.
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