A Simplified 60 Cycle Carrier System Capable of Measuring Low Pressures. ∗

Abstract

Amplification systems for the recording of pulsatile pressure changes using a transducer device have had disadvantages in our hands in ease of operation, stability of the recording mechanism and lack of sensitivity. Previous investigators (1-3) have demonstrated the fidelity and accuracy of resistance wire manometers in the registration of pressure changes derived from intracardiac catheterization technic. Recently, West and associates(4) have described an “inexpensive” carrier amplifier for use with a resistance wire-type manometer and indicated the advantages of such an A.C. amplification system. The following section describes a greatly simplified 60-cycle carrier system of markedly increased sensitivity, which can be phase sensitive and has given satisfactory biological records using a direct recording device without optical magnification.

Description of system. The components of our recording equipment are a Statham P23 A⁺ pressure transducer, a 60-cycle carrier supply system, the balancing network, amplifier, power supply and recorder. Circuit diagrams (Fig. 1 and 2) present the arrangement and design of the apparatus. The power supply is the conventional 400 volt nonregulated and 250 volt regulated type. Line frequency of 60 cycles is fed into the transducer by means of a filament transformer. The transducer output is then fed into a 500 ohm line to grid transformer coupling to a high gain, push-pull amlplifier. A Zero balancing system is also fed into this coupling transformer which acts to balance out the output of the transducer when no pressure is being applied. The signal is picked off the filament transformer used to operate the amplifier filaments. Proper phase is determined by interchanging the primary leads. The zero balancing control is a potentiometer on the output of the balancing amplifier tube. By unbalancing this control or zero set in the proper direction either positive or negative pressures may be recorded; this makes the system phase sensitive.