Technical Specification
ZT-230-0404 E
Noble Gas Monitor FHT 59 ES
Technical Specification ZT-230-0404 E
Noble Gas Monitor FHT 59 ES
Page 1 / 8
1.
Noble Gas Monitor FHT 59 ES
1.1
Introduction
The noble gas monitor FHT 59 E is applied for the automatic monitoring and
early warning of noble gas in work-place air or stack gas.
The sample air is filtered for its aerosol contents and passes through a measuring
vessel. It is fitted with two permanently filled large area proportional counter
tubes mounted on top of it. They detect the beta particles emitted by the noble gas
in the air passing through the vessel. The observed count rate is a direct measure
of the activity concentration of the noble gas. The results are displayed in units of
Bq/m3.
Varying gamma dose rate levels are compensated for by a duplicate anticoincidence circuit.
1.2
System Components
The noble gas monitor FHT 59 ES comprises the following system components:
• measuring channel FHT 1100
• aerosol prefilter
• noble gas detection cell
• 2 proportional counter tubes FH 427 F
mounted onto the measuring vessel in sandwich geometry
• sample air pump
• pressure gauge to control differential pressure
• Sr-90 reference source in slab geometry for functional checks
Technical Specification ZT-230-0404 E
Noble Gas Monitor FHT 59 ES
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1.3
Features
• continuous monitoring of beta emitting noble gas nuclides
• application for work-place and exhaust gas monitoring
• calibration of the monitor for Kr-85 and Xe-133 by an independent institute.
Direct measurement in units of Bq/m3.
• minimized self absorption with the help of a flat measuring vessel (900 ml)
• permanently filled large area proportional counter tubes in sandwich
geometry. No counting gas supply necessary. The background counter tube is
separated from the measuring counter tube by a steel sheet, 2 mm thick.
• measuring channel FHT 1100 with integrated firmware for the evaluation of
the count rates.
• duplicate anticoincidence circuits, i.e. measuring counter tube - background
counter tube and vice versa, suppress varying gamma dose rate levels of up to
100 µSv/h
• low limits of detection by virtue of the "counter mode" with freely selectable
measuring time as well as rapid alarming upon excess of the limit levels
making use of the "ratemeter mode" with variable time constant.
• prevention of aerosol contamination of the measuring vessel with the help of
a grade S aerosol filter
• sample air delivery by maintenance free pump
• 2.5 cm lead shielding to reduce back ground count rate
• compact design in 19"-rack
Technical Specification ZT-230-0404 E
Noble Gas Monitor FHT 59 ES
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1.4
Principle of Measurement
The sample air is sucked in by a maintenance free pump and passes through an
aerosol filter to avoid aerosol contamination in the detection cuvette. Hereafter
the sample air flows through the measuring vessel. The detection volume is flat
(height app. 50 mm) to minimize self absorption. The flow is directed parallel to
the longitudinal axis of the detection cell.
Two permanently filled large area proportional counter tubes in sandwich
geometry are used to detect the noble gas activity. A combined anticoincidence
and difference circuitry of the measurement and the shielding counter tube serves
to reduce the background count rate. The counter tubes are mounted upon one
another and are separated by a sheet, 2 mm in thickness, made of stainless steel.
The complete detector assembly is fixed gas-tight to the measuring vessel by
dismountable clamps. Measuring volume and counter tubes are shielded by
25 mm of lead to reduce the background count rate.
A reference source in slab geometry (Sr-90, 750 Bq) can be inserted into the
measuring vessel for radiological checking purposes.
The counter tube pulses are detected by the charge sensitive preamplifiers of the
detector input I. The preamplified signals are then passed on to the control logic
of the measuring channel FHT 1100. Here, the pulses of the measurement and the
shielding detector are combined via a first anticoincidence stage to reduce the
background count rate. Additionally, a second anticoincidence between the
shielding and the measurement detector is formed. The result of the latter is a
measure of the current back ground count rate of the detection assembly that is
subtracted from the result of the first anticoincidence stage. Therefore, a
background-compensated count rate is obtained that is insensitive against time
dependent gamma dose rate levels of up to 1 µSv/h.
The noble gas activity concentration values can be inferred from the above count
rates with the help of calibration factors for Kr-85 or Xe-133 determined by an
independent institute.
The calculation of the noble gas activity concentration [Bq/m³] is carried out by
the measuring channel FHT 1100.
Technical Specification ZT-230-0404 E
Noble Gas Monitor FHT 59 ES
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1.5
Measuring Electronics FHT 1100
In addition to the power supply and the processor module with RS232/20 mA
serial port (opto couplers), the measuring channel is fitted with the following
modules:
• high voltage max. 4 kV/50 µA, selectable by softkeys in the range of
400 V – 4000 V via D/A-converter
• detector input module I with two counter inputs
• IN/OUT module
− analog output of the activity concentration 0, 4 - 20 mA or 0 - 10 V
− the messages “fail rate, status, alarm activity, alarm concentration“ are
available as potential free relay contacts of the terminal block
The measuring electronics FHT 1100 is operable via 6 soft keys (and a serial port)
and offers the following features:
• display of the of the activity concentration in units of Bq/m³ on LC-display
• selectable alarm level for the filter activity and, separately, for the
concentration plus a detector fail rate alarm
• high voltage setting via softkey
• battery buffered store for 256 sample values
• real time clock
• free setting of the analog output range and of the scaling mode (lin/log)
• optical and acoustical alarming by instrument
• alarming in ratemeter mode selectable between auto reset and manual quitting
• parameter input in dialogue mode
• variable attenuation times for activity and concentration calculation selectable
etc.
Technical Specification ZT-230-0404 E
Noble Gas Monitor FHT 59 ES
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1.6
Sample Air Pump
ELMO gas ring vacuum pump, type 2BH10 with integrated electronics,
operating voltage 14...28VDC,
sample air flow app. 0.6 m3/h
noise level 48 dB(A) at 1m distance.
1.7
Air Flow Measurement and Control
Rotameter with needle valve to set the air flow of app. 0.6 m3/h.
Inductive transducer to signal air flow minimum value.
• air flow (m³/h) min.
1.8
Differential Pressure Sensor
Pressure gauge to control the maximum allowed underpressure against the
detector window due to, e.g. a blocked air inlet. Upon exceeding the maximum
underpressure, the pump is shut down in order to prevent a damage of the detector
window. The signalisation is triggered via the air flow measurement. Reset button
in the front panel to restart the pump after trouble shooting.
1.9
Mains Switch
• mains switch with fuse
• pump switch with fuse
• mains chord, 6 m
1.10
Operation Hours Meter
The monitor is fitted with a non-resettable operating hours meter for the pump
allowing to keep track of maintenance intervals.
Technical Specification ZT-230-0404 E
Noble Gas Monitor FHT 59 ES
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1.11
19” Rack Cabinet 32U
fitted with the above components and a terminal block with potential-free relay
contacts (change-over-relays)
alarm concentration I
alarm concentration II
air flow min.
status ok
detector fail rate
analog output concentration
1.12
max. load of relays:
230 V/6 A
dimension:
width:
600 mm
depth:
800 mm
height: 1600 mm
X
X
X
X
X
0, 4 - 20 mA
Technical Data Noble Gas Monitor FHT 59 ES
aerosol filter
DELBAG glove box filter Akolit B7 DKD
aerosol filter grade S acc. to DIN 24184
measuring vessel
material stainless steel
170 x 100 x 54 mm (length x width x height)
volume 900 ml
shielding
lead, 25 mm
detectors
2 permanently filled proportional counter tubes
FH 427 F in sandwich geometry, separated by a sheet
made of stainless steel, thickness 2 mm
window area
life time
background
156 cm²
> 2 ⋅ 1010 counts
app. 3 s-1
in noble gas detector configuration,
lead shielding 50 mm
noble gas efficiency
Kr-85: 11 %
Xe-133: 5,5 %
Technical Specification ZT-230-0404 E
Noble Gas Monitor FHT 59 ES
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calibration factors
1,00 ⋅ 104 Bq/m³ ⋅ s
2,00 ⋅ 104 Bq/m³ ⋅ s
Kr-85:
Xe-133:
The limits of decision of the activity concentrations acc. to DIN 25482 with a
statistical probability of 5 % for an error of the first kind (false alarm) account to:
Kr-85
Xe-133
0,5 kBq/m³
1,25 kBq/m³
measuring time 3600 s
measuring time 600 s
1 kBq/m³
2,5 kBq/m³
measuring time 3600 s
measuring time 600 s
The limits of detection of the activity concentrations acc. to DIN 25482 with a
statistical probability of 5 % for an error of the second kind (not detected
contamination) are higher by a factor of 2.
measuring range
3,7 ⋅ 108 Bq/m³ related to Xe-133
reference source
Sr-90 app. 750 Bq, slab geometry
sample air pump
ELMO G 2BH10 gas ring vacuum pump
14...28 VDC, motor rating 80 W
operating flow rate 0.6 m³/h
air flow
0.6 m³/h
air flow control
differential pressure gauge
underpressure too high (air intake blocked)
signalisation
5 potential free relay contacts
- noble gas alarm ½
- air flow min.
- status ok
- detector fail rate
data analysis
measuring electronics FHT 1100
ambient conditions
5 °C to 40 °C
860 hPa to 1060 hPa
10 % to 80 %
mains supply
230 V/50 Hz, app. 300 W
cabinet
19“ rack cabinet, 32 U high
temperature
air pressure
relative moisture
Technical Specification ZT-230-0404 E
Noble Gas Monitor FHT 59 ES
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dimensional outline
width
depth
height
weight
app. 200 kg
2.
Reference Source
2.1
Ref. no. SM149475031
Reference Source Sr-90/Y-90, 500 Bq
2.2
Ref. no. P42913110001
Source Holder
60 cm
80 cm
160 cm
Environmental Instruments
Radiation Measurement & Protection
www.thermo.com/rmp
[email protected]
Thermo Electron (Erlangen) GmbH
Frauenauracher Straße 96
D-91056 Erlangen, Germany
+49 9131 909-0
+49 9131 909 475 fax
Post address:
P.O. Box 16 60
D-91051 Erlangen, Germany
Formerly doing business as Thermo Eberline, Bicron RMP, ESM, Harshaw TLD,
Mini Instruments, National Nuclear, NE Technology, Reactor Experiments, Xetex