Electrocardiogram Signal Conditioner
The ECG signal conditioner and electrodes were designed to provide inflight measurements of a crewmember’s ECG activity and to develop a signal wave ranging between 0 and 5 volts peak-to-peak, which is representative of crewman ECG activity. The unit was provided with an adjustment that permitted preflight calibrations. The electrical activity sensed by the body electrode was passed into the signal conditioner which had an input impedance of greater than 40 megohms, and common mode rejection greater than 100 000 to 1. The gain of the signal conditioners was continuously variable from 600 to 4500, and the output was the amplified ECG waveform which varied ±2.5 volts about a 2.5-V bias. Harmonic distortion was less than 1.0 percent over the unit’ls frequency bandpass of 0.2 Hz to 100 Hz. Signal conditioner power of plus and minus 10 VDC at .5 milliamperes was required from the DC to DC converter.
Impedance Pneumograph Signal Conditioner
The ZPN signal conditioner and electrodes were designed for measurement of a change in the transthoracic impedance to a low level current at a frequency of approximately 50 kHz. Measurement was obtained from a pair of electrodes that developed signals (0 to 5 volts peak-to-peak) corresponding to the respiration rate over a wide dynamic range of respiratory activity. The excitation circuit accommodated electrode impedance of 100 to 1000 ohms, and the signal conditioner input impedance was greater than 1 megohm at 50 kHz and greater than 60 megohms in the 0 to 100 Hz frequency range. The output had a range of 0 to 5 VDC with the respiration signal varying about a 2.5-V bias level. Power drain from the DC to DC converter plus and minus 10-V supply was less than 7 milliamps. This unit was also provided with adjustments to accommodate the characteristics of the individual.
Body Temperature System
The body temperature probe and signal conditioner produced an output voltage in the range of 0 to 5 VDC corresponding to sensed temperatures of from 303° to 319° K (85° to 115° F). The system accuracy was within ± 0.17 degree K (± 0.3° F) and had a response time to a 2.8° K (5° F) step change of five seconds. Power requirements were less than 5 milliamps from each of the DC to DC converter supply voltages.