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An inexpensive hot-wire anemometer suitable for behavioral research
Vol. WA. pp. 449 lo 450 1979. Printed m Great Britam
Camp B~ochem. Phwiol.. 0 Pergamon Press Ltd
0300-9629/79/l
IOI-0449102.00/O
AN INEXPENSIVE HOT-WIRE ANEMOMETER SUITABLE FOR BEHAVIORAL RESEARCH DAVID R. BRUMBLEYand EDMUND A. ARBAS Department of Biology, University of Oregon, Eugene, OR 97403, U.S.A. (Received 1 March 1979)
Abstract-l.
Hot-wire anemometers can be used to monitor properties of air current stimuli in behav-
ioral research. 2. Instructions are presented procedures and specifications
for the construction are included.
of an inexpensive
INTRODUCTION
hot-wire
anemometer.
Calibration
it. A simple anemometer was constructed using the exposed filament of an ordinary incandescent lamp as the hot-wire element. Two such lamps were used, one as a sense element, the other as a reference to compensate for fluctuations in temperature, barometric pressure and humidity. The lamps chosen for this anemometer were Chicago miniature type 2102 (1). The bulbs, with attached leads, were mounted in holders made of metal tubing. (In our application, a micromanipulator is used to accurately position the sense probe, and a rigid handle is desired). The glass envelopes of the lamps were then carefully broken by squeezing in a vise. (Protect eyes during this step!) The reference element was isolated from random air currents by covering it with a baffle made of two concentric perforated plastic cylinders with glass wool in between them.
Fast reaction time, high sensitivity and small size make hot-wire anemometers useful for monitoring air current stimuli in behavioral research. Many types of resistive anemometers are commercially available but their cost is often prohibitive for the limited requirements of a small research laboratory. The purpose of this note is to provide the technical data necessary for the construction of an inexpensive hotwire anemometer. This anemometer is used routinely by one of the authors (E.A.) in a study of aerial maneuvering reflexes of locusts. The unit provides a D.C. voltage output proportional to the velocity of air flow, which can be displayed or recorded by common laboratory instruments. THE SENSE ELEMENT
BASIC CIRCUIT
A hot-wire anemometer functions by sensing changes in the resistance of a heated filament caused by the cooling effect of an air current flowing past
A schematic diagram for the anemometer is provided in Fig. 1. The circuit functions as follows: A
150rhcl 114241 1W, Wire Word 2.1 K
Fig. 1. Schematic diagram of the hot-wire anemometer. Al, A2, A3, A4 and each a of a quad operational amplifier. Motorola type MC 3403L. Except where otherwise noted, resistors are $ watt, 5%. 449
DAVID R. BRUMBLEY and
450
constant current is delivered to the reference probe by Ql. Since the probe is protected from air currents, only variations in temperature, pressure and humidity affect the heat loss and thus the resistance of the probe. These variations appear as voltage variations at the (+) input of Al and the top of the sense probe. The bottom of the sense probe is at virtual ground, so it sees the identical voltage as the reference. Resistance variations due to air flow past the sense probe appear as current variations at the (-) input of A2. These current variations are converted by A2 and Q3 to voltage variations and applied to A3. A3 provides gain and offset to the output signal to allow calibration. A4 functions as a comparator and protects the sense probe in the event that the reference probe opens. Should the reference probe open, Ll will light until the reference is restored and the power is momentarily interrupted. An output is provided for the reference probe which can be used to select or match probes. CALIBRATION
PROCEDURES
One method of calibration that has proven successful is to rotate the anemometer sense element at known speeds in still air. We accomplished this by attaching the sense probe to a beam of known length, coupled via an adjustable gear box to a variable speed motor. The electrical output of the probe was coupled to the rest of the circuitry through a Mercotac 590 rotating mercury connector (2). Combinations of gear ratios and motor speeds allowed calibration of the anemometer over a range from OS-16 meters per sec. It is suggested that at least several lamps be purchased, and substituted for the sense and reference probes during calibration. After zeroing the output with the offset adjustment in still air, a notation can
EDMUND A. ARBAS
be made corresponding to the gain setting required for each lamp, to achieve the desired full scale output. This way, recalibration will not be required if either prob,e needs to be replaced, only a change in the setting of the gain adjustment. Alternatively, a large number of lamps, say 25, can be purchased and those with matched resistances chosen for probes. No adjustment is necessary if a probe is replaced with a matched element. Experience with this anemometer has shown that the reference probe rarely fails, but the sense probe. being exposed, is occasionally damaged.
SPECIFICATIONS Range
Response
time
Sensitivity
Linearity Compensation
Power Requirements
0 to 16 meters/second air flow velocity. Less than 2 milliseconds for a 5 meter: second step change in air flow velocity. Maximum of 3 volts/meter!second at 0 velocity, decreasing to 0.1 volts,‘meter/ second at 16 meters;‘second. Linear within 0.4 meters/second from 4 to 14 meters/second. Compensated for temperature to within 0.1 meter/second for temperature = 0 to 50°C. Pressure and humidity not tested. + 15 volts D.C. ((I 150 milliamps regulated.
NOTES
1. Chicago Miniature Lamp Works, 4433 N. Ravenswood Ave., Chicago Ill. 60640, U.S.A. (See catalogue No. 7700 or CMT-3A.) Other lamps can be used with appro-
priate changes to the circuit. 2. Mercotac manufactured by Leslie Mfg. Corp.. Grand, San Marcos, CA 92069, U.S.A. 3. Complete
parts list available
from authors
1025
on request.
Camp B~ochem. Phwiol.. 0 Pergamon Press Ltd
0300-9629/79/l
IOI-0449102.00/O
AN INEXPENSIVE HOT-WIRE ANEMOMETER SUITABLE FOR BEHAVIORAL RESEARCH DAVID R. BRUMBLEYand EDMUND A. ARBAS Department of Biology, University of Oregon, Eugene, OR 97403, U.S.A. (Received 1 March 1979)
Abstract-l.
Hot-wire anemometers can be used to monitor properties of air current stimuli in behav-
ioral research. 2. Instructions are presented procedures and specifications
for the construction are included.
of an inexpensive
INTRODUCTION
hot-wire
anemometer.
Calibration
it. A simple anemometer was constructed using the exposed filament of an ordinary incandescent lamp as the hot-wire element. Two such lamps were used, one as a sense element, the other as a reference to compensate for fluctuations in temperature, barometric pressure and humidity. The lamps chosen for this anemometer were Chicago miniature type 2102 (1). The bulbs, with attached leads, were mounted in holders made of metal tubing. (In our application, a micromanipulator is used to accurately position the sense probe, and a rigid handle is desired). The glass envelopes of the lamps were then carefully broken by squeezing in a vise. (Protect eyes during this step!) The reference element was isolated from random air currents by covering it with a baffle made of two concentric perforated plastic cylinders with glass wool in between them.
Fast reaction time, high sensitivity and small size make hot-wire anemometers useful for monitoring air current stimuli in behavioral research. Many types of resistive anemometers are commercially available but their cost is often prohibitive for the limited requirements of a small research laboratory. The purpose of this note is to provide the technical data necessary for the construction of an inexpensive hotwire anemometer. This anemometer is used routinely by one of the authors (E.A.) in a study of aerial maneuvering reflexes of locusts. The unit provides a D.C. voltage output proportional to the velocity of air flow, which can be displayed or recorded by common laboratory instruments. THE SENSE ELEMENT
BASIC CIRCUIT
A hot-wire anemometer functions by sensing changes in the resistance of a heated filament caused by the cooling effect of an air current flowing past
A schematic diagram for the anemometer is provided in Fig. 1. The circuit functions as follows: A
150rhcl 114241 1W, Wire Word 2.1 K
Fig. 1. Schematic diagram of the hot-wire anemometer. Al, A2, A3, A4 and each a of a quad operational amplifier. Motorola type MC 3403L. Except where otherwise noted, resistors are $ watt, 5%. 449
DAVID R. BRUMBLEY and
450
constant current is delivered to the reference probe by Ql. Since the probe is protected from air currents, only variations in temperature, pressure and humidity affect the heat loss and thus the resistance of the probe. These variations appear as voltage variations at the (+) input of Al and the top of the sense probe. The bottom of the sense probe is at virtual ground, so it sees the identical voltage as the reference. Resistance variations due to air flow past the sense probe appear as current variations at the (-) input of A2. These current variations are converted by A2 and Q3 to voltage variations and applied to A3. A3 provides gain and offset to the output signal to allow calibration. A4 functions as a comparator and protects the sense probe in the event that the reference probe opens. Should the reference probe open, Ll will light until the reference is restored and the power is momentarily interrupted. An output is provided for the reference probe which can be used to select or match probes. CALIBRATION
PROCEDURES
One method of calibration that has proven successful is to rotate the anemometer sense element at known speeds in still air. We accomplished this by attaching the sense probe to a beam of known length, coupled via an adjustable gear box to a variable speed motor. The electrical output of the probe was coupled to the rest of the circuitry through a Mercotac 590 rotating mercury connector (2). Combinations of gear ratios and motor speeds allowed calibration of the anemometer over a range from OS-16 meters per sec. It is suggested that at least several lamps be purchased, and substituted for the sense and reference probes during calibration. After zeroing the output with the offset adjustment in still air, a notation can
EDMUND A. ARBAS
be made corresponding to the gain setting required for each lamp, to achieve the desired full scale output. This way, recalibration will not be required if either prob,e needs to be replaced, only a change in the setting of the gain adjustment. Alternatively, a large number of lamps, say 25, can be purchased and those with matched resistances chosen for probes. No adjustment is necessary if a probe is replaced with a matched element. Experience with this anemometer has shown that the reference probe rarely fails, but the sense probe. being exposed, is occasionally damaged.
SPECIFICATIONS Range
Response
time
Sensitivity
Linearity Compensation
Power Requirements
0 to 16 meters/second air flow velocity. Less than 2 milliseconds for a 5 meter: second step change in air flow velocity. Maximum of 3 volts/meter!second at 0 velocity, decreasing to 0.1 volts,‘meter/ second at 16 meters;‘second. Linear within 0.4 meters/second from 4 to 14 meters/second. Compensated for temperature to within 0.1 meter/second for temperature = 0 to 50°C. Pressure and humidity not tested. + 15 volts D.C. ((I 150 milliamps regulated.
NOTES
1. Chicago Miniature Lamp Works, 4433 N. Ravenswood Ave., Chicago Ill. 60640, U.S.A. (See catalogue No. 7700 or CMT-3A.) Other lamps can be used with appro-
priate changes to the circuit. 2. Mercotac manufactured by Leslie Mfg. Corp.. Grand, San Marcos, CA 92069, U.S.A. 3. Complete
parts list available
from authors
1025
on request.