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Chapter: Medical Electronics : Assist Devices and Bio-Telemetry

Bio Telemetry

Telemetry is a technology that allows remote measurement and reporting of information. The word is derived from Greek roots tele = remote, and metron = measure. Systems that need external instructions and data to operate require the counterpart of telemetry, telecommand.



Telemetry is a technology that allows remote measurement and reporting of information. The word is derived from Greek roots tele = remote, and metron = measure. Systems that need external instructions and data to operate require the counterpart of telemetry, telecommand.


Although the term commonly refers to wireless data transfer mechanisms (e.g. using radio or infrared systems), it also encompasses data transferred over other media, such as a telephone or computer network, optical link or other wired communications. Many modern telemetry systems take advantage of the low cost and ubiquity of GSM networks by using SMS to receive and transmit telemetry data.


·        Bio telemetry is the measurement of biological parameters over long distance.


·        For conveying biological information from a living organism and its environment to a different location where this can be recorded.


·        This involves radio frequency signal as a carrier for modulation, referred to as radio telemetry.





ECG,EEG,EMG- Electrodes act as transducer

For measuring temperatures-Thermisto is used as transducer

For measuring blood pressure-strain gauge  is used as transducer

For measuring stomach pH-glass electrode is used as transducer.





·        Telemetry system should be selected to transmit the bio –electric Signal with maximum fidelity and simplicity.

·        The sysetem should not affect the living system by any interference.


·        Smaller in size light in weight.

·        It should have more stability and reliability.

·        The power consumption at the transmitter and receiver should be small.


·        It should reject common mode interference rejection.

·        Miniatured radio telemetry system should  be used to reduce noise.




·        Single channel telemetry system


·        Multi channel telemetry system




·        For a single channel telemetry system, a miniature battery operated radio transmitter is connected to the electrodes of the patients.


·        The transmitter broadcasts the biopotential to a remote place in which the receiver detects the radio signal and recovers signal for further processing.


·        The receiving system can be located in a room separately from the patients.

·        The only risk is shock to the patient.



·        Biosignal from the patient is converted into electrical signals  by the transducer.


·        They are amplified and filtered at the conditioner. Further they are frequency modulated or pulse modulated.Frequency modulation provides the high noise interference rejection and high stability.


·        The biosignals are amplified to radio frequency range of few hundred KHz to about 300 KHz and then they are transmitted by transmitter antenna.s


·        At radio receiver the corresponding frequency are received and then they are demodulated, amplified and displayed.


Transmission of bioelectric variables:


·        Active measurements


·        Passive measurements Tunnel diode FM transmitter


·        The tunnel diodes exhibit a specific characteristics known as negative resistance. They have extremely low values of inductance an capacitance.


·        It is used for the transmission of EMG,ECG, respiration rates.


·        Tunnel diodes are used as active devices and this circuit has higher fidelity and sensitivity.


·        Total weight is 1.44 gm with battery and the size is small.


·        Varactor diode is basically a reverse biased PN junction which utilizes the inherent capacitance of depletion layer.


·        Varactor diodes are voltage capacitors used for frequency modulation.


·        The signal is transmitted through the inductor L of the tank circuit of RF oscillator.




·        All the signal can be transmitted by using the circuit.

·        No shielded room is needed.


·        Interference is much reduced.


Radio telemetry with sub carrier sytem:


Transmitter side:


·        When the position of transmitter to the body or other conduction object change, the carrier frequency and amplitude will change due to the loading change of the carrier frequency resonant circuit.


·        If the signal has a frequency different from the loading effect ,they can be separated by filters. .Otherwise the real signal will be distorted by loading effect.


·        To avoid this loading effect the sub carrier system is needed. The signal is modulated on a sub carrier to convert the signal frequency to the neighbourhood of the sub carrier frequency.


·        Then the RF carrier is modulated by this sub carrier carrying the signal.

Ø The 20 KHz sub  carrier signal is given to amplitude modulator.

Ø The signals are amplified and  forwarded to the transmitter.

Receiver side:


·        At the receiver end the receiver detects the RF and recovers the sub carrier carrying the signal.


·        At the receiver side, the signals are passed to demodulator, demodulated signal is filtered, amplified by amplifier and then they are given to additional demodulator. It is used to convert the signal from the modulated sub carrier system an to get the original signal.


·        Finally the signal is displayed.




·        For most biomedical applications, simultaneous recording of Bio signals are required for correlation study.


·        Each signal is in need of one channel. When the number of channels is more than the two or three, the simultaneous operation of the several single channel is difficult. At that time multiple channel telemetry system is adopted.


Two types of multiplexing:


1.                 FDM

2.                 TDM

Frequency division multiplex system


·        Each signal is frequency modulated on a sub carrier frequency.

·        Modulated sub carrier frequencies are combined to modulate the RF carrier.

·        At receiver the modulated sub carrier can be separated by the proper band pass filter.

·        Then the each signals are demodulated by using specified frequency.


·        Frequency of the sub carrier has to be carefully selected to avoid interference.


·        The low pass filter are used to extract the signals without any noise. Finally the output unit displays the original signal.


Time division multiplex telemetry system:


·        Most biomedical signals have low frequency bandwidth requirement, we can use time division multiple system by time sharing scheme.


·        Transmission channel is connected to each signal channel input for a short time to sample and transmit that signal.


·        Transmitter is switched to the next input signal channel in a definite sequence.


·        All the channels have been scanned once, a cycle is completed and the next cycle will start. Scanning follows a order from signal 1 to signal 3.

·        At the receiver the process is reversed. The sequentially arranged, signal pulses are given to the individual channels by using gate signal generator.


·        If the number of scanning cycles per second is large and if the transmitter and the receiver are synchronized, the signal in each channel at the receiver side can be recovered. But the scanning frequency has to satisfy the following condition.


fscan = 2fmax


The maximum number of channels practically allowed is smaller than the calculated value of n to avoid the interference between channels.

Advantages of  biotelemetry:


·        Used to record the biosignals over long periods.

·        Patient is not disturbed during recording


·        For future reference or to study the treatment effect

·        Monitor the athletes running a race.

·        For monitoring the persons who are in action the biotelemetry is an ideal one.

·        For recording on animals, particularly for research , the biotelemetry is greatly used.






·        Telemetry is a key factor in modern motor racing, allowing race engineers to interpret the vast amount of data collected during a test or race, and use that to properly tune the car for optimum performance. Systems used in some series, namely Formula One, have become advanced to the point where the potential lap time of the car can be calculated and this is what the driver is expected to meet. Some examples of useful measurements on a race car include accelerations (G forces) in 3 axis, temperature readings, wheel speed, and the displacement of the suspension. In Formula 1, the driver inputs are also recorded so that the team can assess driver performance and, in the case of an accident, the FIA can determine or rule out driver error as a possible cause.

Later  developments  saw  two  way telemetry,  that  allowed  the  engineers  the ability to update calibrations on the car in real time, possibly while it is out on the track. In Formula 1, two-way telemetry surfaced in the early nineties from TAG electronics, and consisted of a message display on the dashboard which the team could update. Its development continued until May 2001, at which point it was first allowed on the cars. By


·        2002 the teams were able to change engine mapping and deactivate particular engine sensors from the pits while the car was on track. For the 2003 season,


the FIA banned two-way telemetry from Formula 1, however the technology still exists and could eventually find its way into other forms of racing or road cars.


·        In addition to that telemetry has also been applied to the use of Yacht racing. The technology was applied to the Oracle's USA-76.




·        Most activities related to healthy crops and good yields depend on timely availability of weather and soil data. Therefore, wireless weather stations play a major role in disease prevention and precision irrigation. These stations transmit major parameters needed for good decisions to a base station: air temperature and relative humidity, precipitation and leaf wetness (for disease prediction models), solar radiation and wind speed (to calculate evapotranspiration), water deficit stress (WDS) leaf sensors and soil moisture, crucial to understand the progress of water into soil and roots for irrigation decisions.



·        Because local micro-climates can vary significantly, such data needs to come from right within the crop. Monitoring stations usually transmit data back by terrestrial radio though occasionally satellite systems are used. Solar power is often employed to make the station independent from local infrastructure.


Water Management


·        Telemetry has become indispensable for water management applications, including water quality and stream gauging functions. Major applications include AMR (automatic meter reading), groundwater monitoring, leak detection in distribution pipelines and equipment surveillance. Having data available in almost real time allows quick reactions to occurrences in the field.


Defense, space and resource exploration systems


·     Telemetry is an enabling technology for large complex systems such as missiles, RPVs, spacecraft, oil rigs and chemical plants because it allows automatic monitoring, alerting, and record-keeping necessary for safe, efficient operations. Space agencies asNASA, ESA, and other agencies use telemetry/telecommand systems to collect data from operating spacecraft and satellites.

Telemetry is vital in the development phase of missiles, satellites and aircraft because the system might be destroyed after/during the test. Engineers need critical system parameters to analyze (and improve) the performance of the system. Without telemetry, these data would often be unavailable




·        In rocketry, telemetry equipment forms an integral part of the rocket range assets used to monitor the progress of a rocket launch. Some special problems are the extreme environment (temperature, accelerations, vibrations...), the energy supply, the precise alignment of the antenna and (at long distances, e.g. in spaceflight) the signal travel time.


Flight Test


·        Flight test programs typically telemeter data collected from on-board flight test instrumentation over a PCM/RF link. This data is analyzed in real-time for safety reasons and to provide feedback to the test pilot. Particular challenges for telemetering this data includes fading, multipath propagation and the Doppler effect. The bandwidth of the telemetry link is often insufficient to transfer all the data acquired and therefore only a limited set is sent to the ground for real-time processing while an on-board recorder ensures the full dataset is available for post flight analysis.


Enemy Intelligence


·        Telemetry was a vital source of intelligence for the US and UK when Soviet missiles were tested. For this purpose, the US operated a listening post in Iran. Eventually, the Russians discovered this kind of US intelligence gathering and encrypted their telemetry signals of missile tests. Telemetry was a vital source for the Soviets who would operate listening ships in Cardigan Bay to eavesdrop on the UK missile tests carried out there.




·        In factories, buildings, and houses, energy consumption of systems such as HVAC are monitored at multiple locations, together with the related parameters (e.g. temperature) via wireless telemetry to one central location. The information is collected and processed enabling intelligent decisions regarding the most efficient use of energy to be implemented. Such systems also facilitate predictive maintenance.


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