Thermal
Conductivity Cell

10 ma.

3
Recorder

Fiaure 2. Diagram of cell bridge circuit.

two hours powered through the converter. Con-
tinuous operation could be extended by placing
more batteries in parallel with the existing bat-
teries. Work is now underway to find a suitable
technique for recording on magnetic tape.

A photograph of the complete apparatus is
shown in Fig. 3. Figure 4 presents a photograph
of the unit in use aboard an airplane in which
it was successfully flight-tested.

Ill. Calibration.

The system was calibrated by introducing
water vapor through the pick-up capsule and

collecting the water vapor in “Drierite”-filled
bottles connected to the exhaust end of the pneu-
matic circuit, Air streams with different water
vapor concentrations were produced by placing
the pick-up capsule over the top of a short plastic
rod which had been drilled to give a series of
concentric chambers. Water was introduced
through the bottom of the assembly with a
syringe. The collection bottles were weighed to
0.1 mgm before and after the collection period.
Recorder deflection in mV was plotted against
the weight of the water collected to yield the
calibration curve shown in Fig. 5.





Fieure 4. Portable evaporative water loss device in use.

5



Fieure 3. Portable evaporative water loss device.

4


REFERENCES

1. Haywoov, H. D. and D, J. SHOEMAKER. “Measure-
ment of Palmar Sweating: Effect of Repeated Meas-
urement from the Same Area.” J. Psychol. 55 :363-369
(1963).

2, Avams, T., G. E, Fuwkuouser, and W. W. Kenpat.
“Measurement of Evaporative Water Loss by a
Thermal Conductivity Cell.” J. Appl. Physiol. 18(6) :
1291-1293. (1968).

3, ApaMs, T., G. E, Funknovser, and W. W. Kenpatt.
“Measurement of Evaporative Water Loss by a
Thermal Conductivity Cell.” OAM Report No. AM
68-25, (1963).

4, Haury, G. T., and T. Apams. “Phase Shifts of the
Human Cireadian System and Performance Deficit
During the Period of Transition: I. East-West
Flight.” OAM Report No. AM 65-28. (1965).

5. Havty, G. T., and T, Apams. “Phase Shifts of the
Human Circadian System and Performance Deficit
During the Period of Transition: II. West-East
Flight.” OAM Report No. AM 65-29, (1965).

6. Haury, G. T., and T. Apams. “Phase Shifts of the
Human Circadian System and Performance Deficit
During the Period of ‘Transition: III. North-
South Flight.” OAM Report No. AM 65-30. (1965).



AM 67-17

A PORTABLE DEVICE FOR THE MEASUREMENT OF
EVAPORATIVE WATER LOSS

G. E. Funkhouser
S. M. Billings

Approved by Released by
o
Vili Pie [USige€ uo
J. Ropert Dintx, M.D. P. V. Smern, M.D.
Cuter, Crvin AEROMEDICAL Feperat Arr Surcron
InstiTuTE

August 1967

FEDERAL AVIATION ADMINISTRATION

Office of Aviation Medicine







mV

mgm/5 min
1.0 2.0 3.0 4.0 5.0

6.0

Flow: 200cc/min
Cell Temp.: 49°C
Bridge Current: 6.2 mA

mgm /min

Figure 5. Calibration curve for portable evaporative water loss device.


on

03

1lF
i

Ql, Q2, Q3 - 2N6E52A

Ri-6000 1/2W

lez yoo
Ye <}ee
D:

* Indicates Selected Component.

DI, 02- Si-50 at IV 200 ma PIV

Q4 -2N383 R2-22000 /2W
QS —2N11838 R3-102701/2W
Clint R4-220
C2-.047 pt RS, R6E- 43000
C3-.022yf R7, RI4,-8200
C4, C5, C6, C7, C8-4.7ut R8-1002
C9-20yf R9- 12K

C10 -500xt RIO -18ka

Fi, F2-.5amp RII-6.801W
TI- YSI Thermister Probe Type 417 RI2-4002 3W

R13-150Q Oven Heater

03, D5,06, D7, D8 - IN2070
D4,-Ge-100 ma at IV 60 PIV
D9-INIS9TA 22v Regulator
S\- Dpst- ON OFF

S2-Dpdt- AC-DC Operation

Fraure 1. Diagram of proportional heater control circuit.
*Reproduced by permission of Hewlett-Packard Com-

pany, Palo Alto, California; modification of Oven
Control Assembly 52434-65T,

12-volt Centralab Power Pack (Crl-1200)
through a Terado 12 V DC to 110 V AC con-
verter (Model 50122).

Air for the pneumatic system is supplied by
a, 96 cubic-inch gas cylinder fitted with a K-valve
and a Cornelius Company pressure-reduction
regulator (Model %). The air passes through a
small cylinder filled with “Drierite” to a Nupro-
fine needle valve (Model B4M), then through
the reference side of the thermal conductivity
cell to the moisture pick-up capsule. The air is

returned from the capsule through the other
side of the cell and is exhausted through a flow
meter. After the proper flow rate is established,
the flow meter is disconnected.

Shielding of electrical connections to the ther-
mal conductivity cell was not necessary, probably
because of the elimination of AC voltage from
the circuits.

The batteries mentioned above will operate
the heater and stirring motor for four to five
hours. The recorder will operate approximately


A PORTABLE DEVICE FOR THE MEASUREMENT OF
EVAPORATIVE WATER LOSS

G. E. Fonxuouser and S. M. Brutres

I. Introduction.

Haywood and Shoemaker have stated, “Many
investigators . . . have demonstrated an increase
in palmar sweating associated with the imposi-
tion of some anxiety-arousing stimulus situation
into the subject’s life." A method for measur-
ing evaporative water loss by using a thermal
conductivity cell as a moisture detector has been
described by Adams et al.?* and has been used
to measure palmar sweat production***, The
method reported by Adams is precise, stable, and
sensitive, but is dependent upon a 110 V AC
power source. This report describes modifica-
tions of the method which permit its use in air-
craft or in other field situations where electrical
power sources are varied or non-existent.

Il. Description.

The original method has been modified to pro-
vide a lighter, smaller, simpler device with self-
contained DC power sources. The modifications
include the use of proportional heater control
and minor changes in the bridge circuit.

The “off-on” type of heater control maintains
a nearly constant temperature more precisely
when the heater voltage is adjusted so that heat
gain in the constant-temperature enclosure is
slightly greater than heat loss. Variations in
environmental temperature consequently necessi-
tate readjustment of the heater voltage to obtain,
maximum control precision. Proportional heater
control, on the other hand, automatically pro-
vides maximum heater output for the initial rise
to operating temperature, and thereafter con-
tinuously adjusts heater voltage to maintain the
operating temperature. Changes in environ-
mental temperatures commonly encountered in
field studies do not affect temperature stability

with this system. The proportional heater con-
trol circuit is shown in Fig. 1.

No temperature indicator has been incorporated
into this unit ; however, a thermistor was mounted
inside the constant-temperature enclosure with
an external jack. The jack provides a means of
connecting a YSI* Tele-thermometer for check-
ing temperature stability when heater malfunc-
tion is suspected.

The bridge for the thermal conductivity cell
has been changed to exclude the potentiometers
for voltage, coarse current, and sensitivity ad-
justments (Fig. 2). The voltage to the bridge
was reduced to six volts, permitting deletion of
the voltage and coarse-current potentiometers.
Sensitivity can still be regulated by varying the
size of the moisture pick-up capsule or by plac-
ing an appropriate resistor in series with the
recorder. The voltmeter in the circuit could
also be eliminated because its only function is a
rapid check of bridge battery condition.

Three six-volt nickel-cadmium batteries (Ev-
eready, N67) were used, one in the bridge circuit
and two connected in parallel to drive a 12-volt
Pittman miniature motor (Model DC-71B) fitted
with a one-inch nylon propeller located inside
the constant-temperature enclosure. Operation
of the fan motor at six volts provides ample
mixing of air. Two 16-volt batteries (Eveready,
N40) were connected in series to the proportional
heater control as shown in Fig. 1. The use of
the 32-volt transformer to operate the heater and
a battery eliminator to drive the stirring motor
prior to actual testing conserves battery power.
At present, recordings are made on a Mosely
strip-chart recorder (Model 680) powered by a

*YSI; Yellow Springs Instrument Co., Yellow Springs,
Ohio.



Qualified requesters may obtain Aviation Medical Reports from Defense Documentation
Center, The general public may purchase from Clearinghouse for Federal Scientific
and Technical Information, U.S. Dept. of Commerce, Springfield, Va. 22151