Chapter 6Telemetry and Data Acquisition

DJM3052

DEM 3A

PN NURUL NADIAH BT SHAHROM

Course Learning Outcomes (CLO)

1) Explain the functions and operational principle of switch, relay, solenoid, electronic control devices, sensor and telemetry system in industrial application. (C3)

3) Demonstrate the understanding of

mechatronic devices. (A3)

Introduction to Data Acquisition System

Data Acquisition: The system of measurement and recording data

Function: use in electronic communication & medical application

Data Acquisition System (DAQ)

D.A.Q

Analog

Wide bandwidth is required

Lower accuracy can be tolerated

Not complex

Digital

Narrow bandwidth

High accuracy and low per-channel cost is required

More complex

Elements of digital-DAQ

Function of each elements:• Transducer – translate physical parameters to electrical signals acceptable by the acquisition system. Some typical parameters include

temperature, pressure, acceleration, weight displacement, and velocity frequency, also may be measured directly.

• Signal conditioner – generally includes the supporting circuitry for the transducer. This circuitry may provide excitation power, balancing circuits, and calibration elements. An example of signal conditioner is a strain- gage bridge balance and power supply unit.

• Scanner or multiplexer – accept multiple analog inputs and sequentially connects them to one measuring instrument.

• Signal converter – translates the analog signal to a form acceptable by the analog-to-digital converter. An example of signal converter is an amplifier for amplifying low-level voltages generated by thermocouples or strain gauges.

• Analog –to-digital (A/D) converter - Converts the analog voltage to its equivalent digital form. The output of the A/D converter may be displayed visually and also available as voltage outputs in discrete steps for further processing or recording on a digital recorder.

• Auxiliary equipment – This section contains instruments for system programming functions and digital data processing. Typical auxiliary functions include linearizing and limit operation. These functions may be performed by individual instruments or by a digital computer.

• Digital recorder – Records digital information on punched cards, perforated paper tape, magnetic tape, typewritten pages, or a combination of systems. The digital recorder may be preceded by a coupling unit that translates the digital information to the proper form for entry into the particular digital recorder selected.

Consequences if auxiliary equipment is not able to operate well

• System programming functions

• Digital data processing

• Linearizing and limit operation

Advantages of transducer in digital DAS

• High operational safety

• Interference reflections rarely trigger the receiver

• Wide measuring range

• High rigidity

• Wide operating temperature range

• Incentive to electric & magnetic field

measurement at a distance

tele

metry

Telemetry

Introduction to Telemetry

Telemetry: A science of measuring at a distanceThe ‘Telemetry’ means measurement at a distance

(tele + metry). The term involves conversion of a quantity into a suitable

signal, the transmission of that suitable signal over a proper channel and its recon version into a display which may be recorded or viewed graphically or may be stored.

Telemetry consist of

Transmitter

Receiver

Channel (connecting transmitter

and receiver)

Telemetry amplitude

Voltage telemetry

The measure is transmitted as a function of ac or dc voltage

A very small current is drawn from the circuit. Resistive drop in the

communication line is negligible. At the receiving end therefore the voltage is

measured by a null method to keep the line current zero at the time of

measurement

Current telemetryThe current in the communication line

is maintained at a measured value, irrespective of the line conditions

Multiplexing

• It is a process of simultaneously transmitting two ormore individual signals over a single communicationschannel.

• It has the effect of increasing the number ofcommunication channels so that more information canbe transmitted.

• This application can save money by using a singlecommunications channel to send multiple informationsignals. Eg: satellite communications – multiplexing isessential to make the system practical & reduce cost

• Eg: Telemetry and telephone

MUX DEMUX

Multiplex input signal

Digital output signal

Multiplexer combines all inputs into a single

signal

Demultiplexer processing input signal by sorting it out into the original individual

signal

Multiplexing

Time division multiplexing (TDM)

Frequency division multiplexing (FDM)

FDM

• FDM is based on the idea that a number of signal can share the bandwidth of a common communications channel.

• Multiple signal to be transmitted over this channel used to modulate a separate carrier. Each carrier comes with different frequency.

• The modulated carriers are added together to form a signal complex signal that is transmitted over the single channel.

FDM block diagram

• Each signal to be transmitted feeds a modulator circuit. • The carriers for each modulation fc is on a different frequency. • The carrier frequencies are usually equally spaced from one another over a

specific frequency range. • Each input signal is given a portion of bandwidth . • Any of the standard kinds can be used including AM, SSB, FM or PM.

TDM

• In TDM , each signal can occupy the entire bandwidth of the channel

• However, each signal is transmitted for only a brief period of time

• In other words, the multiple signals take turns transmitting over the single channel.