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An instrument for measuring the respiration of small animals
Life Sciences No . 10, pp . 779-781, 1963 . Pergamon Press, United States .
Inc . Printed in the
AN INSTRUMENT FOR MEASURING THE RESPIRATION OF SMALL ANIMALS V . Jaclonan, W . C . Barnes, E . G . Erdöl Mellon Institute, Pittsburgh 13, Pennsylvania (Received 24 September 1963) Studies in this laboratory required a sensitive method for assaying the respiration of small animals .
For this purpose, a satisfactory and prac-
tical instrument has been developed here which may be of general interest . The device measures pressure differences in a flow transducer, and converts them into an electrical signal by means of a diaphragm and a differential transformer .
The resulting AC signal is converted to DC signal and registered on a
suitable recorder . A polyethylene tube was inserted in the trachea of rats, guinea pigs and rabbits with the help of tracheotomy . dogs through the
mouth .
The tube was connected to a flow detector which was
bored from a polystyrene rod (Fig . 200 mesh copper screen .
The tracheal tube was introduced in
la) .
The flow of air was restricted with a
The pressure differences were transmitted to the trans-
ducer by a 1/8" polyethylene tube . A sensitive beryllium copper diaphragm is used to convert the pressure differentials of the flow meter into a linear movement (Fig . lb) .
The dia-
phragm is solidly attached to the core of a differential transformer (Schaewitz 033SL) .
The amplitude of the resulting electrical signal depends on the linear
displacement of the differential transformer core .
Standard sensitivity ratios
of the differential transformer are 1 mV output signal/ .001" core movement/1 V transformer excitation . The small counterweight serves to pre-stress the diaphragm and should not be used for zeroing purposes .
Zero adjustment is done by moving a cap
screw ~rttich in turn moves the differential transformer coil into zero position . 779
780
INSTRUMENT FOR MEASURING RESPIRATION
No . 10
v 0 u tr o E cdwo w
d n n 0 t U
u T ~U 00 ~0
_à
0
F
0
No . 10
781
INSTRUN~TP FOR N~ASURII~G RESPIRATION
The electrical circuit is quite simple (Fig . lc) .
The excitation
voltage of the differential transformer is taken from a 6 .3 V filament transformer .
A 5000 ohm 5 watt variable resistor is placed in series with the
differential transformer primary for minor sensitivity adjustments . The low voltage signal received from the differential transformer output is a 60 cycle signal which must be rectified or demodulated to obtain a DC voltage which is suitable for recording in instruments such as the Grass poly graph .
The rectification is accomplished with a Leeds and Northrup No .
chopper (see Fig . lc) .
3338-1
This device is essentially a very fast relay which
switches back and forth at the frequency of the exciting voltage (60 cycles in this case) .
The use of the chopper provides a half wave signal of pulsating
DC which is suitable for a DC recorder input and needs no filtering because the recorder input filter usually is sufficient . The 0 .5 mfd capacitor in the chopper driving circuit serves a dual purpose .
First,
it sets the phase or the time of the chopper contacts properly,
then it drops the supply voltage from 110 V to the 27 V needed to drive the chopper . During testing, sensitivities of 1 mV per 0 .6" of water pressure were easily obtained with the device and signal frequencies of 100 cps were clearly distinguished with a Grass polygraph recorder . The routine operation of the instrument is relatively simple and trouble-free .
Inc . Printed in the
AN INSTRUMENT FOR MEASURING THE RESPIRATION OF SMALL ANIMALS V . Jaclonan, W . C . Barnes, E . G . Erdöl Mellon Institute, Pittsburgh 13, Pennsylvania (Received 24 September 1963) Studies in this laboratory required a sensitive method for assaying the respiration of small animals .
For this purpose, a satisfactory and prac-
tical instrument has been developed here which may be of general interest . The device measures pressure differences in a flow transducer, and converts them into an electrical signal by means of a diaphragm and a differential transformer .
The resulting AC signal is converted to DC signal and registered on a
suitable recorder . A polyethylene tube was inserted in the trachea of rats, guinea pigs and rabbits with the help of tracheotomy . dogs through the
mouth .
The tube was connected to a flow detector which was
bored from a polystyrene rod (Fig . 200 mesh copper screen .
The tracheal tube was introduced in
la) .
The flow of air was restricted with a
The pressure differences were transmitted to the trans-
ducer by a 1/8" polyethylene tube . A sensitive beryllium copper diaphragm is used to convert the pressure differentials of the flow meter into a linear movement (Fig . lb) .
The dia-
phragm is solidly attached to the core of a differential transformer (Schaewitz 033SL) .
The amplitude of the resulting electrical signal depends on the linear
displacement of the differential transformer core .
Standard sensitivity ratios
of the differential transformer are 1 mV output signal/ .001" core movement/1 V transformer excitation . The small counterweight serves to pre-stress the diaphragm and should not be used for zeroing purposes .
Zero adjustment is done by moving a cap
screw ~rttich in turn moves the differential transformer coil into zero position . 779
780
INSTRUMENT FOR MEASURING RESPIRATION
No . 10
v 0 u tr o E cdwo w
d n n 0 t U
u T ~U 00 ~0
_à
0
F
0
No . 10
781
INSTRUN~TP FOR N~ASURII~G RESPIRATION
The electrical circuit is quite simple (Fig . lc) .
The excitation
voltage of the differential transformer is taken from a 6 .3 V filament transformer .
A 5000 ohm 5 watt variable resistor is placed in series with the
differential transformer primary for minor sensitivity adjustments . The low voltage signal received from the differential transformer output is a 60 cycle signal which must be rectified or demodulated to obtain a DC voltage which is suitable for recording in instruments such as the Grass poly graph .
The rectification is accomplished with a Leeds and Northrup No .
chopper (see Fig . lc) .
3338-1
This device is essentially a very fast relay which
switches back and forth at the frequency of the exciting voltage (60 cycles in this case) .
The use of the chopper provides a half wave signal of pulsating
DC which is suitable for a DC recorder input and needs no filtering because the recorder input filter usually is sufficient . The 0 .5 mfd capacitor in the chopper driving circuit serves a dual purpose .
First,
it sets the phase or the time of the chopper contacts properly,
then it drops the supply voltage from 110 V to the 27 V needed to drive the chopper . During testing, sensitivities of 1 mV per 0 .6" of water pressure were easily obtained with the device and signal frequencies of 100 cps were clearly distinguished with a Grass polygraph recorder . The routine operation of the instrument is relatively simple and trouble-free .