counter at the time of testing. The change of +400 Hz is the information frequency change brought about by the change in strain or temperature measured by the sensor. It is this information frequency change that the discriminators isolate as a dc voltage change, which is proportional to the measured strain and is recorded the oscillograph. 77. 8 Calibration Batteries are calibrated under simulated service conditions for voltage drop versus time. Bridge-controlled transmitters are calibrated for strain subcarrier frequency change using a cantilever beam instrumented with esistance strain gauges. The beam is calibrated for load versus strain using a strain ator. It is then used to calibrate the bridge-controlled transmitters statically, by measuring the subcarrier frequency change as a function of strain. A dynamic calibration can also be made by using a second cantilever beam driven by a vibration generator. Two resistance strain gauges are mounted back-to-back on the second beam and calibrated. One of the gauges is monitored through the telemetry system and the other by wire link to the oscillograph and the two signals are then compared. The single-resistance strain gauge transmitter is similarly calibrated, but in this case, the beam is fixed in a fatigue machine operating at 30 Hz. Calibrations are performed at various strain levels. Again, two calibrated gauges are monitored and compared, one using the telemetry systems and the other using wire link. The effect of temperature on a transmitter and battery is measured at temperatures from 65 to 135F by placing both in an air-circulating oven, with the receiving equipment and the calibration beams to room The voltage-controlled transmitter is calibrated for temperature subcarrier frequency change from 78 to 40F. Two calibrated thermocouples, welded next to one another on a piece of stainless steel, are heated simultaneously. After determining by wire link instrumentation that both thermocouples are indicating the ame temperature, the millivolt output of one is fed into the transmitter, and the output of the other is fed by wire into a precision potentiometer. The subcarrier frequency change is determined as a function of temperatur and the radio signal is recorded on the calibrated oscillograph, with a galvanometer determining its deflection as a function of temperature. The data obtained by wire link and radio are then compared to establish the calibration. The effect of thermocouple lengths can also be investigated in the same test setup. The receivers and discriminators are calibrated before these tests Cold junction compensation may be investigated from -40 to 258F by cooling the transmitter and battery, with leads shorted and with a 20-mV input, in a cold chamber below room temperature and by heating in an ir-circulating oven to above room temperature. The 20-mV input is imposed with a dc power supply kept outside the temperature chamber. The discriminators are calibrated with the transmitters. The subcarrier frequency, which is the input to the discriminator, is monitored with a digital counter as the calibration beam is loaded. The voltage output orresponding to the frequency change can be monitored with a vacuum tube voltmeter. The strain, subcarrier frequency change, and the voltage output of the discriminator are then correlated. a digital frequency counter is used to set the transmitter center frequen 77.9 Telemetry Frequency Allocations Frequency bands for telemetry have been allocated as follows: 88-108 MHz Low power, noninterference 216-260 MHz General telemetry 400-475 MHZ Command destruct 1435-1540 MHz General telemetry 1710-1850 MHz Video telemetry 2.2-2.3GHz General telemetry e 2000 by CRC Press LLC© 2000 by CRC Press LLC counter at the time of testing. The change of ±400 Hz is the information frequency change brought about by the change in strain or temperature measured by the sensor. It is this information frequency change that the discriminators isolate as a dc voltage change, which is proportional to the measured strain and is recorded on the oscillograph. 77.8 Calibration Batteries are calibrated under simulated service conditions for voltage drop versus time. Bridge-controlled transmitters are calibrated for strain subcarrier frequency change using a cantilever beam instrumented with resistance strain gauges. The beam is calibrated for load versus strain using a strain indicator. It is then used to calibrate the bridge-controlled transmitters statically, by measuring the subcarrier frequency change as a function of strain. A dynamic calibration can also be made by using a second cantilever beam driven by a vibration generator. Two resistance strain gauges are mounted back-to-back on the second beam and calibrated. One of the gauges is monitored through the telemetry system and the other by wire link to the oscillograph, and the two signals are then compared. The single-resistance strain gauge transmitter is similarly calibrated, but in this case, the beam is fixed in a fatigue machine operating at 30 Hz. Calibrations are performed at various strain levels. Again, two calibrated gauges are monitored and compared, one using the telemetry systems and the other using wire link. The effect of temperature on a transmitter and battery is measured at temperatures from 65 to 135°F by placing both in an air-circulating oven, with the receiving equipment and the calibration beams to room temperature outside the oven. The voltage-controlled transmitter is calibrated for temperature subcarrier frequency change from 78 to 640°F. Two calibrated thermocouples, welded next to one another on a piece of stainless steel, are heated simultaneously. After determining by wire link instrumentation that both thermocouples are indicating the same temperature, the millivolt output of one is fed into the transmitter, and the output of the other is fed by wire into a precision potentiometer. The subcarrier frequency change is determined as a function of temperature, and the radio signal is recorded on the calibrated oscillograph, with a galvanometer determining its deflection as a function of temperature. The data obtained by wire link and radio are then compared to establish the calibration. The effect of thermocouple lengths can also be investigated in the same test setup. The receivers and discriminators are calibrated before these tests. Cold junction compensation may be investigated from –40 to 258°F by cooling the transmitter and battery, with leads shorted and with a 20-mV input, in a cold chamber below room temperature and by heating in an air-circulating oven to above room temperature. The 20-mV input is imposed with a dc power supply kept outside the temperature chamber. The discriminators are calibrated with the transmitters. The subcarrier frequency, which is the input to the discriminator, is monitored with a digital counter as the calibration beam is loaded. The voltage output corresponding to the frequency change can be monitored with a vacuum tube voltmeter. The strain, subcarrier frequency change, and the voltage output of the discriminator are then correlated. A digital frequency counter is used to set the transmitter center frequency. 77.9 Telemetry Frequency Allocations Frequency bands for telemetry have been allocated as follows: 88–108 MHz Low power, noninterference 216–260 MHz General telemetry 400–475 MHz Command destruct 1435–1540 MHz General telemetry 1710–1850 MHz Video telemetry 2.2–2.3 GHz General telemetry