User Manual

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IPN 074-289L

Composer Operating Manual

2.6 Description of Subsystems

The two major components which comprise the Composer are the Transducer

and the Controller.

2.6.1 Transducer

IPN 761-601

The basic Transducer element is the resonant chamber with the inlet and outlet

tubes providing a means of transporting the gasses from the reactor’s supply

lines, through the transducer’s case and finally connecting to the structure that

defines the shaped resonant chamber, see Figure 2-6. Because the speed of

sound of a gas is dependent on it’s temperature there is a mechanism to

measure and control the temperature. First, a platinum resistance thermometer,

or PRT, is imbedded into the chamber body. Two low power heater elements are

able to provide a "heat only" means of control. The PRT and heaters are

connected in a feed back control loop that is monitored and executed by the

controller portion of the instrument system. A thermo-mechanical switch (not

shown) is attached to the chamber body and automatically interrupts the

heaters’ current should there ever be a fault that would allow the temperature

to exceed 70° C. Both ends of the resonant chamber are defined by a tensioned

diaphragm. This diaphragm is used to safely seal the chamber and also to

provide a level of flexibility sufficient to impose an acoustic wave on one end

and to allow its transport and detection outside the resonant chamber on the

other end.

The function of all of the above component elements is to provide an ideal

environment for transporting and measuring sound velocity through the

resonant chamber.

The sending microphone cartridge provides the source of acoustic energy to

excite the diaphragm. It is designed to effectively couple acoustic energy into

the diaphragm yet not couple energy into the chamber body. It uses a pair of

flat response electro-dynamic microphones to accomplish this. This cartridge is

The receiver microphone cartridge is used for detection of the acoustic energy

transported across the resonant chamber and through the diaphragm. It is a

wide response electret type with a built in FET amplifier. Its signal is amplitude

detected by the controller portion of the instrument system.