A TELEMETERING THERMOMETER 
by DR. ANGELO J. CAMPANELLA, Senior Physicist 
HRB-Singer, Inc. 
State College, Pennsylvania 
ABSTRACT 
A temperature transducer for temperature 
measurement at depth for a radio telemetering 
link from a drift buoy has been developed. The 
nominal design depth is 200 meters for the 
transducer. It has an accuracy of 0, 1°C or 
better depending on radio link quality. The 
system is operational and has been tested at 
shallow depths, approximately 4 meters, by the 
Woods Hole Oceanographic Institute, 
INTRODUCTION 
Radio drift buoys currently in Gee provide 
a means for tracing the motion of surface waters 
in the open sea. No information concerning the 
identity of the water in which the buoy rests at 
the moment of observation is available other than 
that accumulated from past sampling. In drift 
experiments it is important to know whether the 
buoy has remained with the water mass in which 
it was deposited or conversely to know some 
parameter of the water immediately under it. 
Surface temperature is relatively meaningless 
due to environmental influences. The tempera- 
ture at a depth of 200 meters is suitable for the 
purposes of identification since it lies below the 
daily, and most seasonal, influences. A length 
of multi-conductor cable that is suitable for 
suspension at this depth is well-logging cable, 
The temperature can be measured to 1G) or 
better depending upon the radio link signal-to- 
noise ratio. The unit has been laboratory 
calibrated from 0° to 30°C and is repeatable to 
within .03°C. The response time for a temper- 
ature excursion from room temperature to 0°C 
is about one minute for 2% full scale accuracy 
and about one hour for the remainder, all within 
calibration accuracy. The longer lag is due to 
the temperature coefficient of the Mylar ca- 
pacitors in the Wien Bridge. The response 
time can be reduced to a few seconds by simple 
design improvements. 
COMPONENT DESCRIPTION 
BUOY 
The drift buoy developed by Franz, Walden, 
and Ketchem is shown in Figures | and 2. 
Figure 3 is a block diagram of this system. 
its quiescent state the receiver is tuned toa 
radio frequency of 2398 KC. Whena radio 
signal modulated by the proper audio tone is 
picked up by the antenna, one of two resonant 
In 
39 
reed relays is actuated, depending on the par- 
ticular tone, and a sequence of events then 
occurs. If the first relay is actuated, the call 
sign of the buoy is transmitted in international 
morse code in A-] emission(CW), followed by a 
long dash. If the second relay is actuated by the 
proper tone, either a long dash, or some special 
signal is transmitted, 
For the telemetering thermometer application 
this buoy was used ina slightly modified form 
which included the attachment of a temperature 
transducer. The mode of transmission was 
changed to F-1 (frequency shift keying). The 
mark-space rate of shifting was made to depend 
on the temperature at the depth of the transducer. 
FSK modulation is used due to its FM-like noise 
rejection and good anti-fade qualities, 
To effect F-l modulation of the transmitted 
signal, several components were added to the 
crystal oscillator circuit. See Figure 4, A 300 
picofarad capacitor was placed between the 
2398 KC crystal and ground, The final R.F. stage 
is allowed to run continually, and the diode across 
the capacitor self biases itself to a high im- 
pedance. When the keying contacts close, the 
diode CR2 no longer can bias itself and conse- 
quently shorts the 300 picofarad capacitor. The 
carrier frequency is then shifted 140 cps lower 
in frequency. Crystal diode CR3 and the .001 
capacitor isolate the circuits from the keying 
leads, and hence remote keying is possible. To 
produce conductance switching, a transistor can 
adequately replace the relay in this operation. 
TRANSDUCER SUSPENSION 
Short length of BT wire is used for suspension 
of the pressure case for shallow water so that no 
mechanical support is required from the con- 
ducting cables. See Figure 2. No difficulty is 
anticipated for the 200 meter suspension es- 
pecially since it comprises not a mooring but 
merely a suspension for the pressure case plus 
whatever weight is needed to maintain a suitably 
vertical wire angle in the presence of current 
shear. Extra flotation may be required at the 
surface buoy to support this. 
Electrical leads were brought through the 
heavy top plate by water-tight connection and a 
joint made with a Joy 3-prong connector, A 3- 
conductor cable ran down to the temperature 
transducer and terminated in a Joy single contact 
pressure connector. Although a sea return or 
suspension cable could have been used as one lead, 
