The precise temperature control of ball SAW sensors for trace moisture
measurement at ppb level of concentration
Yusuke Tsukahara, Kazushi Yamanaka, Nobuo Takeda, Shingo Akao, Toru Oizumi, Hideyuki Fukushi, ToshihiroTsuji
Ball Wave Inc.
2017/6/20 Ball Wave Confidential 1
Process Industry : A 10
The ball SAW sensor
• What is the ball SAW sensor?
• How does it measure the trace moisture?
• We had a difficulty caused by temperature variation.
• How did we solve it?
• Our detection limit is about 1ppbV trace moisture in N2 gas.
• We detect the trace moisture in hydrocarbon gases with a same calibration curve.
• We detect a-few-seconds spikes of trace moisture.
2017/6/20 Ball Wave Confidential 2
What is the ball SAW sensor?
Piezoelectric
Sphere
Sensitive
Film
Interdigital
Transducer
SAW
Long propagation
⇒High sensitivity
Molecules
2017/6/20 Ball Wave Confidential 3
(Surface Acoustic Wave)
SAW goes around and around and around the sphere.
What is the ball SAW sensor?
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Piezoelectric
Sphere
Sensitive
Film
Interdigital
Transducer
SAW
Long propagation
⇒ High sensitivity
Molecules
Time of
1 turn
Without Gas
With Gas
Without Gas
With Gas
Time
Time of
100 turns
Amorphous silica film
stiffens when it absorbs
water molecules.wet
dry
wet
dry
water
Amorphous silica
Quartz crystal 1~3mm in diameter.
How does it measure the trace moisture?
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TCXO
ADC1
FDIV
SwitchTxRx
Ball SAW sensor
BPF 2+
BPF1
Synthesizer
A
BPF1
BPF2 ADC2 C
FDIV
BPF3
BPF4 D B
Amp Amp
FDIV
How does it measure the trace moisture?
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We measure
(1) the decay rate and
(2) delay-time of pulses.
Difficulty caused by temperature variation.
• We have to measure the ppm level of change in the delay-time of pulses.
• But the delay-time strongly depends on temperature.
• We need to compensate it for the trace moisture detection at ppbV level.
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How did we solve it?
2017/6/20 Ball Wave Confidential 8
13 13.1 13.2 13.3
−500
0
500
−200
0
200
13 13.1 13.2 13.3
−20
0
20
Am
plit
ude
(mV
)Time (μs)
Am
plit
ude
(mV
)
80 MHz
240 MHz
Wavelet transform
Waveform at 4th turn
We use two frequencies to
compensate for the temperature
variation.
How did we solve it?
2017/6/20 Ball Wave Confidential 9
)()()( REF111 TTAwGfTBt -+=D
)()()( REF222 TTAwGfTBt -+=D
)()()( 1212 wGTBCfftCttW -=D-D=D
Cff
ttffTTAtT
-
D-D=-=D
)/(
)/()(
12
2112REF1
[ ])273(/exp)()( B12 +D=- TkaTBCff e
From these equations, we obtain
Relative delay time changes at frequencies 1f and 2f , are given by
where w and T are moisture
concentration and temperature,
respectively.
where
and C=A2/A1.
Ref: Proceedings of Symposium on Ultrasonic Electronics, Vol. 37 (2016) 16-18 November, 2016
6/20/2017 Ball Wave Confidential 10
Falcon Trace (code name)
We implemented the method
in a prototype.
Our calibration curves for high end and low end
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Decay rate due to moisture dB Delay time ratio of two frequencies
Our detection limit is about 1ppbV.
2017/6/20 Ball Wave Confidential 12
Trace moisture measurement
in the nitrogen gas
Trace moisture in hydrocarbon gases.
• It works in hydrocarbon gases with the same calibration curve.
2017/6/20 Ball Wave Confidential 13
-20%
0%
20%
40%
60%
80%
100%
120%
0 60 120 180 240 300 360 420 480 540 600
TIME (sec)
PH
AS
E S
HIF
T
N2 100sccm
H2 100sccmCH4 75sccm
C2H6 51sccm
Transient Characteristics @ 1,800ppm H2O Injection
Trace moisture in hydrocarbon gases.
2017/6/20 Ball Wave Confidential 14
MFC
MFC
Ball SAW
N2
H2
CH4
C2H6
・・・
Exhaust
0.07 to 0.998 L/min
0.002 to 0.03 L/min
1 L/min
Rotary
Valve
Dry Gas line
Wet Gas line
~3 m
~0.3 m
Bubbler
0 ℃
Saturated vapor pressure
@0 ℃ = 611 Pa
40 to 2000 nmol・mol-1 H2O
MFC
0.1 L/min
H2O Vapor Generation Case 1: Bubbler Method
Trace moisture in hydrocarbon gases.
2017/6/20 Ball Wave Confidential 15
-20%
0%
20%
40%
60%
80%
100%
120%
0 60 120 180 240 300
TIME (sec)
PH
AS
E S
HIF
T
N2 100sccm
H2 100sccmCH4 75sccm
C2H6 51sccm
Transient Characteristics @ 1ppm H2O Injection
Trace moisture in hydrocarbon gases.
2017/6/20 Ball Wave Confidential 16
MFC
MFC
Ball SAW
Exhaust
0.1 L/min
0.1 L/min
1L/min
Rotary
Valve Dry Gas line
Wet Gas line
~3 m
H2O
nW
Diffusion Tube
nW = DWSe / LRT
L
e
~0.3 m
N2
H2
CH4
C2H6
・・・
1 nmol・mol-1 H2O
H2O Vapor Generation Case 2: Diffusion Tube Method
A-few-seconds spikes in the trace moisture.
2017/6/20 Ball Wave Confidential 17
• Injected dry N2 gas and 10ppmv wet N2 gas alternatively in 5 seconds into the sensor cell.
dry N2
wet N2
sensor cell
90mm
PC
A-few-seconds spikes in the trace moisture.
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Background is not an artifact but is due
to the adsorption of moisture on the
inner surface of piping.
-65℃ FP
-90℃ FP
2017/6/20
A-few-seconds spikes in the trace moisture.
Ball Wave Confidential 19
90mm
PC A dry chamber
The ball SAW sensor works with 0 flow rate.
The open-face sensor
A-few-seconds spikes in the trace moisture.
2017/6/20 Ball Wave Confidential 20
90mm
PC
We can monitor a leakage in a moment.
leak
A dry chamber
The open-face sensor
Thank you for listening.
• We offer a unique solution for the trace moisture measurement with
versatile capabilities.
• A prototype for commercial model is available now for early access.
2017/6/20 Ball Wave Confidential 21