Instrument includes four temperature-sensing, Y-cut quartz crystals to determine wind direction, velocity, and temperature. Two additional AT-cut crystals are used to determine air humidity. Entire signal processing is provided by built-in electronics circuits

Lave, E. G.

Stephens, J. B.

English

NASA Technical Reports Server

Screen 
AT-Cut 
Crystals 
June 1975	 B75-10124 
NASA TECH BRIEF 
NASA Pasadena Office 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Quartz Crystal Microbalances To Measure Wind Velocity and Air Humidity 
Two new quartz crystal microbalance (QCM) 
instruments are proposed which can measure wind 
velocity, direction, and temperature as well as air 
humidity all in one package. Separate instruments 
have been used previously by meteorologists and 
Incoming
Wind
air-quality researchers to measure each of these 
quantities. 
A simplified schematic of one of the new 
instruments is shown in the illustration. The 
instrument includes four temperature-sensing, Y-cut 
Screen 
.
I 'II V-Cut 
I	 It-- — Crystals 
I	 I
ii11 Electronics 
Screen
and Heater
I	 I V-Cut 
I	 IL 
I _L____:pjI Crystals V I	 I I	 I. Screen J 
I II I r-fi--I I 
I	 III	 I 
:
HtiII1 
Screen	 r1I- 
	
I	 I 
	
— 1	 I	 Ii 
.
Screen 
it Crystals 
tronics 
Heater 
Plug (Power 
and Signal) 
Humidity Determining 
Crystals in Perforated Plate 
led Plate 
Simplified Instrument Schematic
(continued overleaf) 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Adr?iinistration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights. 
Convective
Flow
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quartz crystals to determine wind direction, velocity, 
and temperature. Two additional AT-cut crystals are 
used to determine air humidity. The entire signal 
processing is provided by built-in electronics circuits. 
Each of the first four crystals is connected to an 
oscillator. The oscillators operate at different 
fundamental frequencies in the 5-MHz band so that 
different outputs can be easily distinguished. The 
crystals have a temperature coefficient of approxi-
mately 400 Hz/°C and the instrument can resolve 
temperature changes as small as 0.010 C. 
The instrument is enclosed on four sides by a series 
of screens. The screens are designed to admit wind 
into the instrument without obstruction. Inside the 
instrument is a 0.1-W heater which generates warm 
air current. This air current, forming a vertical stream 
by convection, is sufficient to raise crystal tempera-
ture by 0.5° C. 
As the wind strikes the instrument, the air current 
is deflected downstream of the wind. This changes the 
temperature level of each crystal. As a result of the 
temperature changes, the frequencies of the oscillator 
circuits are shifted by different magnitudes. 
Three parameters are determined from these fre-
quency shifts: 
1. Wind direction is determined by recording new 
oscillator frequencies. Each unique frequency 
combination is indicative of a specific wind 
direction. 
2. Wind velocity is determined by observing the 
magnitudes of the frequency shifts. Large shifts 
indicate high wind velocity. 
3. Wind temperature is obtained by summing the 
frequency shifts and comparing with the initial 
ambient-temperature frequency outputs. 
Humidity is measured by the two AT-cut crystals. 
Again, each crystal is connected to an oscillator. One 
crystal is coated with a hydrophobic substance, and 
the other is coated with .a hydrophilic substance. 
When the air humidity is zero, the two oscillator
outputs are identical. In the presence of humidity, 
moisture is absorbed by the hydrophilic substance; no 
moisture collects on the other crystal which remains as 
a reference. The collected moisture causes a slight 
change in mass on the crystal; this change in mass 
causes a shift in its oscillator frequency. Air humidity 
is determined directly based on the frequency 
difference between the two crystals. 
The second quartz crystal instrument is similar to 
the one described. In addition to measuring wind 
velocity and air temperature, the second system can 
also measure solar irradiance. This makes it more 
complete for meteorological applications. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: TSP75-10124 
Patent status: 
This invention is owned. by NASA, and a patent 
application has been filed. Inquiries concerning non-
exclusive or exclusive license for its commercial 
development should be addressed to: 
Patent Counsel 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Source: James B. Stephens and

Eric G. Laue of
Caltech/JPL
under contract to

NASA Pasadena Office

(NPO-13462)
is 
Categories: 03 (Physical Sciences) 
B75-10124	 02 (Electronics Systems)


Quartz crystal microbalances to measure wind velocity and air humidity

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