Tribo-electric dust monitoring explained
Explore a tribo-electric dust monitor. See how contact and induction charge from dust particles become a calibrated mg/m3 reading, and when that reading stops being valid.
Charge. Signal. Calibration.
Inside a tribo-electric dust monitor.
An insulated rod in the duct picks up charge from every particle that touches it or flies past it.
See how that charge becomes a mg/m³ reading, and where the reading stops being trustworthy.
Follow the charge
Particles in. A charge signal out.
- Dust particle
- Contact, DC
- Induction, AC
- Signal path
Explore the monitor
About this model
The reading is the AC signal divided by the site calibration factor. It is only valid while the process stays within the conditions of that calibration: the QAL2 runs, the yearly AST and the QAL3 zero and span checks exist to prove exactly that.
Model assumptions
AC signal ∝ concentration × velocity, DC signal ∝ concentration × velocity^1.5. The calibration factor is fixed at the reference conditions (dry gas, 12 m/s, clean rod); deviations are shown as reading error rather than corrected. Coating reduces the DC channel by up to 60 % and the AC channel by up to 10 %. Wet gas attenuates the AC channel and adds noise.
Particle size and material also change the charge per particle; the model uses one representative dust. The reference port stands for the gravimetric method (EN 13284-1) used in the QAL2 calibration and the AST. The zero / span check replaces the probe signal by an internal test signal for a few seconds, as the QAL3 procedure does; it checks the electronics, not the calibration.
Real instruments filter and average the AC signal over tens of seconds and apply a site-specific, sometimes non-linear, calibration function.
Charge from every particle.
Particles that hit the rod hand over charge (DC). Particles that only pass nearby induce a charge that flips sign as they move away (AC). The AC channel is the one that survives a dirty rod, so certified monitors use it.
Signal to mg/m³ by calibration.
The charge amplifier delivers a raw signal. Parallel isokinetic reference runs (EN 13284-1) fix the relation between that signal and the dust mass, the QAL2 calibration of EN 14181. Without it the monitor is a trend indicator.
Valid only under the same conditions.
Change the velocity, the dust type or let the gas get wet, and the calibration no longer applies. Try the sliders: the operating point leaves the calibration line while the true concentration stays put.