BAI 9128 Moving Filter Monitor

The BAI 9128 moving filter monitor is an easy transportable monitor intended for the measurement of α- and β-particulates. The BAI 9128 features a compact design and high performances, similar to those obtained with stationary monitors operating at higher flow rates. The unit runs without maintenance for prolonged periods.





  • Detection limit according DIN 25482, at 1 h collection and measuring time for β < 0.04 Bq/m3 for α < 0.004 Bq/m3
  • Si-CAM- detector 600 mm2 for simultaneous α-β-measurement
  • Compensation for natural activity 
  • Measurement of ambient dose rate
  • Measurement of natural activity (Radon - Thoron progeny)
  • Separate warning beacon with 10 m cable
  • Selectable filtertape advance speed (5, 10 mm/h)
  • Filtertape autonomy up to 10 months, filter change warning before end of tape
  • Pump unit with flow low check
  • Low pump noise level

The BAI 9128 moving filter monitor collects and measures air from rooms, ducts or the environment for the presence of Alpha and Beta particulates.

The compact design integrates a sampling head with detector, the pump unit and the control electronics in a standard 19” cassette.

An S-class glass fiber filter-tape collects the sample air particulates. This filter-tape advances at a programmable continuous speed eliminating the need for frequent filter replacement due to dust loading.

A rugged Silicon detector allows to measure both Alpha and Beta particulates. The Silicon detector is installed above the dust collection area at close distance to the filter, and delivers optimal Alpha & Beta counting performance. Radon progeny is eliminated from the gross Alpha Beta activity using Pseudo-coincidence gating or Beta/Alpha ratio compensation methods. Downstream of the filter a silent pump unit ensures a stable flow rate of 3 m3/h.

As evaluation electronics the data logger LB 5340 as well as the LB 5310 or LB 9000 could be used. The electronics allows the user to measure the presence of radioactive aerosols as well as the ambient dose rate and to trigger alarms above certain levels. The healthy status of the overall system is continuously monitored.



Structural shape

19”cassette 6HU


483 x 264 x 320 mm3

elapsed hour counter

flow low

filter trouble indicators (led)

fast filter advance pushbutton

reset filter timer push button

plexi door for access wetted parts

Dust collection area25 x 25 mm2
Wetted parts mat´lNi plated brass to MIL stdrd
Construction mat´lAlum side & back plate, plexi cover front
Sampling section  
from inlet to filter
 to DIN 25423 (06/96) stainless steel RS 316L



940 – 1100 hPa

–150 mbar to atm. pressure




0 to +40 °C

-20 to +40 °C




0 – 95 % RH non condensing

0 – 95 % RH non condensing
















Glas fibre Particulates filter to DIN S&S N° 10, roll 40 m x 50 mm, core 25 mm dia



speed selectable 5/10 mm/h

fast 500 mm/h pushbutton frontpanel

Autonomy> 10 months at 5 mm/h speed
Controls                                Filter ruptured, Filter supply low (< 3 m)






Pump Unit

low maintenance (> 10 000 h)

silent operation (< 55 dB(A) at 1 m)

pump head max -440 mbar

typical operating -160 mbar

Flow ratetypical 3.3 m3/h at NTP



pump head pressure switch (flow low)

typical set point 3.2 m³m/h at NTP







Alpha-Beta Detector
TypeSi-CAM 600 m² light tight

Typical efficiencies

solid sources




20 % / 4 pi





25% / 4 pi

10% / 4 pi

Energy range

(preamp threshold setting)



100 keV - 2 MeV

3 MeV - 9 MeV

Background in system




< 0.002 cps

< 0.2 cps

Leadshield2 cm / 4 pi
Ambient gamma sensitivityBeta channel < 0.4 cps per µSv/h 137Cs radiation


Type                                    LB 2029 preamplifier with built-in dual pulse height discriminator













Alarm Unit
Type                                         LB 9128-ALARM, green system healty lamp, yellow, red, blue flashing lamps, resetable horn 90 dB(A) at 1 m
Lampsba 15d/230-260V/5 - 7 W
Functions             Reset horn, lamp test pushbutton
Connectionsmains 230 VAC connector,
remote signals DIN T 3406 6 pole male






Overal Electrical Specifications
Mains                         230VAC/50 Hz/Single phase, I nom 1 A,
Fuse : 1.6A T, thermal safety 1.3A



General Applications
All applications where airborne α and β particulates radioactivity has to be measured. To prevent personnel exposure. To measure release rates in ducts and stacks.

  • Decommissioning
  • Nuclear power
  • Source manufacturing
  • Industrial safety
  • Research


Specific Applications
In hostile environments where a moving filter monitor has advantages:


Workplace or stack monitoring with high dust concentrations

  • Decommissioning with abrasive material removal
  • Titrituration process monitoring
  • Phosphate manufacturing
  • Waste disposal sites
  • Fuel reprocessing


Where space is at a premium

  • Mobile labs
  • Intervention vehicles


Where movable intervention equipment is needed

  • On the spot monitoring
  • Temporary access gates to contaminated areas
Format Size
BAI 9128 en PDF 294.64 KB