Process Industry : A 10

The precise temperature control of ball
SAW sensors for trace moisturemeasurementat ppb level of concentration
Yusuke Tsukahara, Kazushi Yamanaka, Nobuo Takeda, Shingo
Akao, Toru Oizumi, Hideyuki Fukushi, ToshihiroTsuji
Ball Wave Inc.

2022/9/22

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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.
2022/9/22

Ball Wave Confidential2What is the ball SAW sensor?
Piezoelectric
SphereSensitive
Film

Molecules

SAW (Surface Acoustic Wave)

Interdigital
TransducerLong
propagation
SAW goesaround and aroundand aroundthe sphere.
⇒Highsensitivity

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3What is the ball SAW sensor?
QuartzcrystalPiezoelectric

1~3mm in diameter.

SphereAmorphoussilica
SensitiveSAWFilm

water Molecules

Interdigital
TransducerLong propagation
High sensitivity

wet GasWithout
With dryGas
wet GasWithout
With dryGas

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Amorphous silica film
stiffens when it absorbs
water molecules

Time of
1 turnTime of
100 turns

Time
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4How does it measure the trace moisture?
TCXO

Synthesizer
FDIV
FDIV

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FDIV

BPF3

ADC1

D BPF4 C

ADC2

BPF1
BPF 2+BPF1

Amp AmpA
B BPF2
SwitchRx Tx
Ball SAWsensor

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2798

Appl.How
Phys. Lett.,
Vol.it76,
No. 19, 8 Maythe
2000trace moisture?
doesmeasure

2798

Appl. Phys. Lett., Vol. 76, No. 19, 8 May 2000

Yamanaka, Cho, and Tsukahara

We measure(1) the decay rate and(2) delay-time of pulses.
FIG. 2. Observed signal of SAW with a large number of monotonicallydecaying pulses.

FIG. 3. Expanded wave forms of SAW at !a" the first turn and !b" thetwelfth turn.

larly to the surface of a ball. Due to the interference of thetwo laser beams with different optical frequencies, scanninginterference fringes were produced. By adjusting the mechanical stages, the average spacing of the fringes was madeequal to the wavelength of the SAW, and the scanning velocity of the fringes was made equal to the phase velocity of
the SAW, in order to establish an approximate phase matching. The laser has a specially designed long pulse width ofBall Wave Confidential
around 100 ns, to allow a long interaction time between thefringes and the SAW. The long interaction time is essential

The similarity of the two signals is important for precise
time interval measurements when we apply the pulse echo
overlap method or the cross correlation method. To test thesimilarity, we tried to overlap the signals by shifting thetwelfth signal to the first signal. When the shift was 93.470#s, the phase of the twelfth signal lagged slightly behind thatof the first signal, as shown in Fig. 4!c". When the shift wasincreased by 8 ns, the phase of twelfth signal was slightly
ahead of that of the first signal, as shown in Fig. 4!a". However, when the shift was 93.474 #s, a value calculated fromFIG. 2.2022/9/22
Observed signal of SAW with a large number of monotonically

FIG. 3. Expandedwave
6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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We use two frequencies tocompensate for the temperature
variation.

Amplitude (mV)

How did we solve it?
500

Waveform at 4th turn0−500
1313.1

13.2

13.3

Wavelet transform

Amplitude (mV)

20080 MHz0−20020240 MHz0−2013

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13.1
13.2
Time (μs)

13.38How did we solve it?
Relative delay time changes at frequencies f1 and f 2 , are given by
Dt1 = B(T ) f1G(w) + A1(T - TREF)
Dt2 = B(T ) f2G(w) + A2 (T - TREF )From these equations, we obtain
DtW = Dt2 - CDt1 = ( f 2 - Cf1 ) B(T )G(w)where w and T are moistureconcentration and temperature,
respectively.

( f 2 / f1 )Dt1 - Dt2
DtT = A1 (T - TREF ) =( f 2 / f1 ) - C

where ( f2 - Cf1 ) B(T ) = a exp[De / kB (T + 273)]
and C=A2/A1.

Ref: Proceedings of Symposium on Ultrasonic Electronics, Vol. 37 (2016) 16-18 November, 2016
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9Falcon Trace (code name)We implemented the method
in a prototype.

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10Our calibration curves for high end and low end

Decay rate due to moisture dB

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Delay time ratio of two frequencies

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Our detection limit is about 1ppbV.
Trace moisture measurementin the nitrogen gas

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12Trace moisture in hydrocarbon gases.
• It works in hydrocarbon gases with the same calibration curve.
("#$:"/(##133;
6"/(##133;<6%/=*133;<"6&/*(133;(##$Transient Characteristics@ 1,800ppm H2O Injection

5678./86,9+

'#$
&#$
%#$
"#$
#$!"#$#

2022/9/22&#("#('#"%#)##)&#+,-./01234%"#%'#*%#

Ball Wave Confidential&##13Trace moisture in hydrocarbon gases.
H2O Vapor Generation

MFC

Case 1: Bubbler Method

Dry Gas line

0.1 L/minBall SAW

RotaryValve

MFC
MFC

0.07 to 0.998 L/min
0.002 to 0.03 L/min

Wet Gas line

~0.3 m40 to 2000 nmol･mol-1 H2O~3 m

Bubbler

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N2H2CH4C2 H6･･･

0℃

Saturated vapor pressure@0 ℃ = 611 Pa

1 L/minExhaustBall Wave Confidential

14Trace moisture in hydrocarbon gases.
("#$9".(##022:5".(##022:;5%.<=022:;"5&.=(022:(##$4567-.75+8*'#$

Transient Characteristics@ 1ppm H2O Injection&#$%#$"#$#$!"#$#&#("#('#"%#)##*+,-./0123

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Trace moisture in hydrocarbon gases.
H2O Vapor Generation Case 2: Diffusion Tube Method

MFC

0.1 L/min

Dry Gas line

0.1 L/min

Wet Gas line

MFCnW

1 nmol･mol-1 H2OBall SAW

RotaryValve~0.3 m~3 mL

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N2H2CH4C2 H6･･･

Diffusion TubenW = DWSe / LRTe
H2O

1L/minExhaustBall Wave Confidential

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A-few-seconds spikes in the trace moisture.
• Injected dry N2 gas and 10ppmv wet N2 gas alternatively in
5 seconds into the sensor cell.
90mm

PCsensor cell
dry N2wet N22022/9/22

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A-few-seconds spikes in the trace moisture.
Background is not an artifact but is dueto the adsorption of moisture on theinner surface of piping.

-65℃ FP-90℃ FP

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A-few-seconds spikes in the trace moisture.
The ball SAW sensor works with 0 flow rate.

A dry chamber

90mm

PCThe open-face sensor

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A-few-seconds spikes in the trace moisture.
We can monitor a leakage in a moment.

A dry chamber

90mm

PCleakThe open-face sensor

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20Thank you for listening.
• We offer a unique solution for the trace moisture measurement withversatile capabilities.
• A prototype for commercial model is available now for early access.

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