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PCME SENSOR TECHNOLOGY

The more you learn about PCME sensor technology, the more you will be convinced that they offer unique capabilities.

 

  

 

 

 

Dust passing by and colliding with a rod in the stack or duct produces an electrical signal that is relative to the concentration of dust.  This is known as the TRIBOELECTRIC EFFECT.  The probe electronics read the current produced between the probe and ground.  Standard triboelectric sensors use the DC component of the signal, which is produced mainly by those particles that collide with the probe.

          

 

PCME uses a patented AC signal processing technique that primarily measures the signal produced by those particles that flow past the probe.  This ELETRODYNAMIC signal processing technique overcomes some known problems associated with particles colliding  with the probe velocity sensitivity and dust build-up.  Unlike DC systems, the electrodynamic (AC) measurement is not significantly affected by velocity changes in the range of 24 to 60 ft/sec.  Also, because it does not rely primarily on collisions, the electrodynamic signal is not affected by dust build-up on the probe.

 

EPA’s Bag Leak Detection Guidance (developed using older DC technology) states that

you should wait several days after installation to allow the dust build-up on the probe to stabilize.  This waiting period is not necessary for the PCME electrodynamic probe.

 

The electrodynamic principle provides a more stable signal.  The graphs to the right show trend graphs from an AC and a DC sensor on the same duct.  The DC signal has less zero stability and seems to indicate a problem where there is none.

 

          

Another advantage that PCME has over other sensors is that we use digital communications.  The raw signal is digitized at the probe before it is sent to the control unit.  Other systems carry the raw analog DC signal (remember it is in picoamps) over a cable to the control unit.

 

 

The EPA Bag Leak Detection Guidance requires that users check the zero and span of the sensor at least once each month.  On other systems this is accomplished manually using a special signal generator.  The PCME DT990 uses a patented method for automatically checking the zero and span calibration of the sensor.  

 

The probe is electronically isolated from  the signal processing electronics and a zero and upscale 

signal are applied to both the main probe and the check (contamination) probe.  The results are 

made available at the control unit.  The system is initially configured to conduct this test once every two hours, but the user may change the cycle time.  If a calibration result is outside the specification, a fault alarm (contact closure) is generated and logged in the controller memory.  The numerical results are displayed alternately with the “Pass” or “Fail” message.

 

          

 

 

How does the DT990 sensor check for dust build-up on the probe?  

 

Although dust buildup on the probe rod itself is not a problem with the PCME sensor, excessive dust build-up on the probe insulator can be a problem (as with other triboelectric systems).  PCME uses a patented Contamination Check to detect bridging of current across the insulator.  When the two signals converge, this indicates bridging.  When the contamination result reaches the point where there might be a significant effect, an alarm is activated and logged.

          

 

 

 

You can download a whitepaper that describes Electrodynamic Technology.

 

   Electrodynamic