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.

2017/6/20

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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.
2017/6/20

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

Molecules

SAW (Surface Acoustic Wave)

Interdigital
Transducer
SAW goesaround and around andLong
propagation
around thesphere.
⇒Highsensitivity

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3What is the ball SAW sensor?
QuartzcrystalPiezoelectric

1~3mm in diameter.

SphereAmorphoussilica
Sensitive

SAWFilm

water Molecules

Interdigital
TransducerLong propagation⇒ High sensitivity

wet GasWithout
With dryGas
wet GasWithout
With dryGas

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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5How does it measure the trace moisture?

We measure(1) the decay rate and(2) delay-time of pulses.

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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 transformAmplitude (mV)

200

80 MHz0−20020240 MHz0−20132017/6/20

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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 ) f 2G(w) + A2 (T - TREF)

From these equations, we obtain

where w and T are moistureconcentration and temperature,
respectively.

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

DtW = Dt2 - CDt1 = ( f 2 - Cf1)B(T )G(w)where ( f 2 - 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, 20162017/6/20

Ball Wave Confidential

9Falcon Trace (code name)We implemented the method
in a prototype.

6/20/2017Ball Wave Confidential

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.
120%
N2 100sccm
H2 100sccm
CH4 75sccm
C2H6 51sccm

100%

PHASE SHIFT

80%

Transient Characteristics@ 1,800ppm H2O Injection

60%
40%
20%0%-20%0

2017/6/20

60

120

180

240

300
360
TIME (sec)

420

480

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540

600

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Trace moisture in hydrocarbon gases.
H2O Vapor GenerationMFCCase 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 mBubbler

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N2H2CH4C2H6･･･

0℃

Saturated vapor pressure@0 ℃ = 611 Pa

1 L/minExhaustBall Wave Confidential

14Trace moisture in hydrocarbon gases.
120%
N2 100sccm
H2 100sccm
CH4 75sccm
C2H6 51sccm

100%

PHASE SHIFT

80%

Transient Characteristics@ 1ppm H2O Injection

60%
40%
20%
0%-20%060120180

240

300

TIME (sec)2017/6/20

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

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 mLDiffusion TubenW = DWSe / LRTe

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N2H2CH4C2H6･･･

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 in5 seconds into the sensor cell.
90mm

PCsensor cell

dry N2wet N2

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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 the
inner 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.

90mm

A dry chamber

PC
The open-face sensor

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

90mm

A dry chamber

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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