pittcon 2002
TRANSCRIPT
Environmentally Robust CarbonMonoxide Sensor for Fire Detection
Dr. Neils R.S. Hansen& Dr. Ann M. Harvey
Objective“ To develop a quality CO sensor made via a
robust automated manufacturing process.”
Portable Gas Detection
Flammable Gas Detection
Toxic Gas Detection (Semiconductor)
BRAND NAMES
Residential Gas Detection
Sensor Supplier
UK’s No. 1 manufacturer & supplier of residential carbon monoxide (CO) alarms, 1.5 M units sold since 1996.
UK Headquarters, Poole, England
We manufacture both CO detectors & sensors to pass BSI, UL & CSA standards
Approximately two million cells sold since 1996. Only CO cell used presently for fire detection.
World’s largest gas detection company.
DESIGN STRATEGY
Critical analysis of existing products and processes
Improve performance to meet more stringent certification approvals introduced since 1996
Design for automation
Failure Modes and Effects Analysis
Failure rate in field use is < 0.05 %
Process : poor sealing due to manual errors
Effects Zero CO sensitivity ( filter blockage ) False alarms ( corrosion currents )
Complete customer satisfaction demands the effective elimination of these failure modes from the ECO-Sure(TM) cell design.
Design : electrolyte leakage in extreme R.H.
Analysis of CO Cells ( End-of-Life after ~ 5 yrs in field use )
0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5
CO Cell Lifetime (years in field use)
Nor
mal
ised
Sen
sitiv
ity (
% o
f ini
tial)
Predicted Sensitivity DecayMeasured Decay of Old ProductPredicted Ecosure Decay
Performance Requirements
Improved baseline stability
Wider operational humidity rangeHigh R.H. = no electrolyte leakageLow R.H. = improved span stability
Increased physical and chemical filtration capacity
Reduced cost of work in progress
Design for Automation
Patented design has fewer components for automated manufacture
Efficient use of all components Charcoal cloth acts as a filter, an electrode support and also an efficient
gassing plenum Wick acts as both an electrolyte reservoir and compresses the electrode
stack Separator preferentially draws electrolyte from the wick and electrically
isolates electrodes
Materials have all been proven historically over five years
Previous Design
Pt Working Electrode
Plastic HousingImpregnated CharcoalCloth Filter (2 layer)
Wick
Pt Counter Electrode
Push-fit Pins
Electrolyte
ECO-Sure(TM) DesignPlastic Housing
Impregnated CharcoalCloth Filter (5 layer)
Pt Working Electrode
Wick
Pt Counter Electrode
Insert-moulded Pins
Separator Electrolyte
Theoretical Electrolyte Volume vs Relative Humidity
0
10
20
30
40
50
60
70
80
90
100
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
Relative Humidity ( % at 20 oC )
Elec
trol
yte
Volu
me
( % o
f cel
l fre
e vo
lum
e )
0
1
2
3
4
5
6
7
8
9
10
11
12
Con
cent
ratio
n (m
ol d
m-3
)
ECO-Sure Electrolyte Volume Electrolyte Concentration
maximum capacity
Equilibrium humidity of injected electrolyte
ECO-Sure(TM) Cells During High Humidity Storage
0
10
20
30
40
50
60
70
80
90
100
110
0 5 10 15 20
Time ( weeks )
Nor
mal
ised
Sen
sitiv
ity (
% )
0.0
0.1
0.2
0.3
0.4
0.5
Wei
ght C
hang
e ( g
)
ECO-Sure cell sensitivity
Mean ECO-Sure weight change
48 ECO-Sure(TM) cells stored at 96% R.H and 20oC
UL TestFailure
ECO-Sure(TM) Cells During Low Humidity Storage
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25
Time ( weeks )
Nor
mal
ised
Sen
sitiv
ity (
% )
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
Mea
n W
eigh
t Cha
nge
( g )
ECO-Sure cell sensitivity
Mean ECO-Sure weight change
48 ECO-Sure(TM) cells stored at 11% R.H and 50oC
UL TestFailure
More efficient use of electrode allows a 16 % reduction in the area of the cap hole
ECO-Sure(TM) Cap Assembly
Old Design Cap Assembly
2 layer charcoal cloth
5 layer charcoal cloth
X-sections
Cross Sensitivity Comparison ( Old Design vs ECO-Sure(TM) )
90
60
4
15
40.5 0.53
0
10
20
30
40
50
60
70
80
90
100
800 ppm NO2 ( VdS ) 2000 ppm Ethanol(EN50291)
50 ppm SO2 ( VdS ) 200 ppm IPA ( UL2034)
Gas Applied
Res
pons
e ( C
O p
pm e
quiv
alen
t )
Old designECO-Sure
PASS criteria is < 36 ppm CO equivalent
Improved Baseline Temperature Stability Effect : Positive Baseline Drift at elevated temperature
Effect : Negative Baseline Drift at elevated temperatures
Comparative Baseline Drift PerformanceOld Design = + / - 8 ppm CO equivalent(acceptable for residential CO monitoring)ECO-Sure(TM) < + / - 2 ppm CO equivalent(required for fire detection applications)
Cause : As manufactured organic contamination de-sorbs from the filter.Solution : Condition cells at elevated temperature prior to release
Cause : VOCs out-gassing from potting compound
Solution : Improved curing regime
Baseline Temperature Drift of ECO-Sure(TM) Cells
-2
-1
0
1
2
3
4
5
6
0 5 10 15 20 25 30
Time ( hours )
Res
pons
e ( C
O p
pm e
quiv
alen
t )
-20
-10
0
10
20
30
40
50
60
Tem
pera
ture
( C
elsi
us )
Temperature
Mean Baseline DataMaximumMinimum
Baseline Temperature Shock of ECO-Sure(TM) Cells
-2
-1
0
1
2
3
0 1 2 3 4 5 6 7 8 9 10
Time ( hours )
Bas
elin
e D
rift (
CO
ppm
)
-40
-30
-20
-10
0
10
20
30
40
50
60
Tem
pera
ture
( C
elsi
us )
Mean Baseline DriftMaximum Drift ( Mean + 2 x s.d. )Minimum Drift ( Mean + 2 x s.d. )Temperature
Baseline Temperature Shock of ECO-Sure(TM) Cells
0
5
10
15
20
25
30
35
40
0 1 2 3 4 5 6 7 8 9 10
Time ( hours )
Bas
elin
e D
rift (
CO
ppm
) Threshold Alarm Gas Concentration
ECO-Sure(TM) Product SummarySemi-automated production since March 2001 Two stages of process FMEA fed into automated production line Yields are recorded for continual process improvement
ECO-Sure(TM) cells have been approved in instruments tested to : BS, LPC, VdS & UL2034 (due April, 2002)
UL Component Recognition Advanced recognition scheme, monthly linearity test, maximum
concentration measurement and continuous 15 ppm CO exposure Provisional recognition granted (Feb 2002) achieved on first submission
Automated Manufacture
Quality Improvements ( Components ) Cleanliness Dimensional tolerance Placement
Quality Improvements ( Process ) Thermal welding of electrode followed by 100 % leak testing Electric welding and continuity testing of every current collector Every critical operation has a minimum of one verification check SCADA system monitors and reports production status
Consistent high quality of manufacture
Product Summary
Product currently supplied in volume to multi-national fire and residential CO detector manufacturers
Significant investment in automation to improve manufacturing process and increase throughput
Significant improvement in cell performance to significantly exceed all current standards