Introduction toIntroduction to Data Acquisition SystemsData Acquisition Systems

NIDHIN MANOHARNIDHIN MANOHAR

A System that :A System that :• acquires measurement data from acquires measurement data from

the process / field instrumentsthe process / field instruments • To displays the data / parameters To displays the data / parameters • Process dataProcess data • Store dataStore data• Provide output signals to external Provide output signals to external

Indicator / control devicesIndicator / control devices• makes data available for other makes data available for other

functionsfunctions

Data Acquisition System Data Acquisition System Is a Generic term forIs a Generic term for

DAS : Why do we use them?DAS : Why do we use them?

• Large number of measurement points, Large number of measurement points, • large volume of computations, large volume of computations,

processing and conversions,processing and conversions,• complicated computations,complicated computations,• transients measurement, transients measurement,

• improve response to events / alarms,improve response to events / alarms,

• simultaneous recordings,simultaneous recordings,

• reduce / avoid manual data loggingreduce / avoid manual data logging• reduce human decision making,reduce human decision making,• improve safety,improve safety,

• monitor over long duration,monitor over long duration,• facilitate remote telemetry,facilitate remote telemetry,• connectivity to SCADA or existing connectivity to SCADA or existing

MIS systemsMIS systems• Strict sequence of operations and Strict sequence of operations and

controls ,controls ,• Interfacing to sensors, transducers, Interfacing to sensors, transducers, • eliminate indicators, electronics,eliminate indicators, electronics,• eliminate T&M Instruments,eliminate T&M Instruments,• improve documentationimprove documentation

DAS : Why do we use them?DAS : Why do we use them?

Data Acquisition SystemData Acquisition System

Data acquisition system, in effect, requires Data acquisition system, in effect, requires integration of:integration of:

• Sensor/transducer for measurement of Sensor/transducer for measurement of physical variables physical variables

• Signal-Conditioner/transmission circuitry, Signal-Conditioner/transmission circuitry, that enables conversion of signal outputs that enables conversion of signal outputs from transducers to a readable form for from transducers to a readable form for Data Acquisition/interface modules.Data Acquisition/interface modules.

• The Data Acquisition Hardware The Data Acquisition Hardware comprising Multiplexer, Amplifier, A/D comprising Multiplexer, Amplifier, A/D Converter, Buffer Memory, etc. to digitise Converter, Buffer Memory, etc. to digitise the analog signals for CPU.the analog signals for CPU.

• Computer/CPU to process the digital data Computer/CPU to process the digital data for data processing, display, outputs for data processing, display, outputs (control), storage, transmission, etc.(control), storage, transmission, etc.

Process MeasurementsProcess Measurements

Temperature, Pressure, Load, Force, Temperature, Pressure, Load, Force,

Displacement, Speed, Acceleration, Displacement, Speed, Acceleration,

Flow, Level, density, viscosity, Flow, Level, density, viscosity,

analytical parameters such as pH, ORP, analytical parameters such as pH, ORP,

Conductivity, turbidity, BOD, etc., Conductivity, turbidity, BOD, etc.,

Light/Dark sensors, gas-composition Light/Dark sensors, gas-composition

analyzers / Chromatographs, etc..analyzers / Chromatographs, etc..

Other parameters include gas-leak Other parameters include gas-leak

detectors, fire/smoke detectors, power detectors, fire/smoke detectors, power

quality, energy, quality, energy,

• PCs are affordable,PCs are affordable,• large variety of interfaces,large variety of interfaces,• software and operational flexibility,software and operational flexibility,• large storage capabilities,large storage capabilities,• reasonably good data processing reasonably good data processing

capabilities,capabilities,• user-friendly,user-friendly,• ease of portability to other systems,ease of portability to other systems,

PC based Data AcquisitionPC based Data Acquisition

PC InterfacingPC Interfacing

• Add-On Card Plug-in Slots,Add-On Card Plug-in Slots,

• COM ports (RS-232C); further add COM ports (RS-232C); further add Modem for long distances,Modem for long distances,

• Universal Serial Bus (USB), Universal Serial Bus (USB), • Parallel Port (Centronics / Printer),Parallel Port (Centronics / Printer),• LAN / Ethernet (TCP/IP) interface,LAN / Ethernet (TCP/IP) interface,

• Add GPIB or IEEE-488 Interface,Add GPIB or IEEE-488 Interface,

• Add SCSI or may be built-in,Add SCSI or may be built-in,

• Add HART, FIELDBUS or other Add HART, FIELDBUS or other InterfacesInterfaces

• AnalogAnalog

outputsoutputs from transmitters / from transmitters / meters for pressure, meters for pressure, temperature, level, strain-gage, temperature, level, strain-gage, load/force, flow, displacement, load/force, flow, displacement, etc. etc. Eg: 4 to 20mA, mV or VEg: 4 to 20mA, mV or V

Signal

SignalPVPV

• DigitalDigitalPulse outputsPulse outputs : :

Turbinemeters, Positive displacement Turbinemeters, Positive displacement meters,meters,

Encoders, Tachometers, etc.Encoders, Tachometers, etc.

Hi/Lo or ON/OFF signalsHi/Lo or ON/OFF signals: :

Limit-switches, micro-switches, photo-Limit-switches, micro-switches, photo-sensors, proximity sensors, Open-sensors, proximity sensors, Open-collector outputs, relays, etc. collector outputs, relays, etc.

Serial Serial : :

RS232C, RS485, USB; HART, MODBUS, RS232C, RS485, USB; HART, MODBUS,

FieldBus, Ethernet, etc.FieldBus, Ethernet, etc.

Parallel dataParallel data: :

IEEE-488, Parallel port, etc.IEEE-488, Parallel port, etc.

ON/OFF or ON/OFF or OPEN/CLOSE OPEN/CLOSE type Signalstype Signals

Pulse or Pulse or Frequency Frequency SignalsSignals

Outputs from Data Acquisition & Outputs from Data Acquisition & Control SystemsControl Systems

• AnalogAnalog4 to 20mA control signals4 to 20mA control signals for for

Pneumatic actuated controlPneumatic actuated control

valves, Controller Set-point , etc.valves, Controller Set-point , etc.

4 to 20mA or V4 to 20mA or V signalsignal to output flow / to output flow / other parameters to remote indicators other parameters to remote indicators or chart-recordersor chart-recorders

• Digital (High speed) Outputs : Pulse / Digital (High speed) Outputs : Pulse / FrequencyFrequency

Output for remote totaliser / counter.Output for remote totaliser / counter.

Output to speed and motion control systems;Output to speed and motion control systems;

Output to Stepper-motor based systems.Output to Stepper-motor based systems.

• Digital (Low-speed) OutputsDigital (Low-speed) Outputs

Control outputs to Relays, Actuators, Control outputs to Relays, Actuators,

ON/OFF control for Motors/ Pumps, ValvesON/OFF control for Motors/ Pumps, Valves

Status and Alarm Outputs to remote / panel Status and Alarm Outputs to remote / panel

mounted indicators, and annunciators.mounted indicators, and annunciators.

Sensor/Transducer selection:Sensor/Transducer selection:

• sensors, transmitters and signal sensors, transmitters and signal conditioners best suited for the conditioners best suited for the application to be chosen.application to be chosen.

• existing meters may need replacement if existing meters may need replacement if there is no suitable output signals.there is no suitable output signals.

When trying to Set Up your own D.A.SWhen trying to Set Up your own D.A.S

• Mobility (for PC, transducers, etc)Mobility (for PC, transducers, etc)• Normal PC? Laptop, Industrial PC? What Normal PC? Laptop, Industrial PC? What

costs?costs?• Cable-routes to D.A.S? Data Quality, Cable-routes to D.A.S? Data Quality,

Costs?Costs?• Distances involved? No. of cable runs? Distances involved? No. of cable runs?

Type of signals? Wireless options? Type of signals? Wireless options? Costs?Costs?

• Signal conditioning options, costs?Signal conditioning options, costs?

Performances, Economics?Performances, Economics?

• where to locate DAS?where to locate DAS?• Where are the field devices? Where are the field devices? • How is the Environment?How is the Environment?

– Dirt, moisture, temperature , etc. Dirt, moisture, temperature , etc. – AC Mains power (Voltages AC Mains power (Voltages

fluctuations? Surges/spikes?)fluctuations? Surges/spikes?)– shock and vibration.shock and vibration.

• Can normal PC be used? whether Can normal PC be used? whether additional protection necessary?additional protection necessary?

• Can enclosures help? IP required?Can enclosures help? IP required?

Main Considerations: D.A.SMain Considerations: D.A.S

• Rugged SMPS (wide ACV range)• redundancy : hot-swappable SMPS• additional cooling fans with dust

filters• isolation of plug-in boards, CPU-

board, disk drive, etc., from shock • disk-drive bays with covers • membrane-sealed keyboards.• Ingress protection (IP)

Industrial PCIndustrial PC

Analog Input Interface:Analog Input Interface:

• 12 to 24-bit resolution ADCs

• No. of channels : 8, 10,16, 20, 32, or 64, per board.

• Speed : 100k, 110k, 330k, 500k, 1.25M, 5M, 20M samples per second.

• Resolution Vs Speed.

Selection of DAS hardwareSelection of DAS hardware

A/D Converter Resolution

Sampling FrequencySampling Frequency• Aliasing

– Acquired signal gets distorted if sampling rate is too small.

Analog Inputs:Analog Inputs:

• Continuous high-speed data acquisition : on-board FIFO RAM

• Simultaneous sampling : multiple ADCs

• Low-level signal inputs : gains

Selection of hardwareSelection of hardware

Digital to Analog Conversion:

• generally one output channel; • Analog output boards may have 2,

4 or more analog outputs

Selection of hardwareSelection of hardware

Digital Input/Output:

• usually TTL compatible (0-5V)• direct 12V or 24V Input-Output: if

built-in Optical-Isolation • Reed-Relays, SSR: 1 to 3A NO

Contacts. • No. of Digital IO: 4, 8, 16, or 24

Selection of hardwareSelection of hardware

Counter-Timer Functions:

• event or pulse counting• frequency measurement• pulse output: used in stepper

motor control, other control applications.

• Single-pulse output• Time measurement (gated)• Internal clock: 10kHz, 100kHz,

1MHz, 10MHz or 20MHz.

Selection of hardwareSelection of hardware

PC Specifications:PC Specifications:

• Ports, Slots, interfacesPorts, Slots, interfaces• Storage. (HDD, Flash)Storage. (HDD, Flash)• on-line processing. ( RAM)on-line processing. ( RAM)• Graphical content / updates.Graphical content / updates.• DAS software requirements.DAS software requirements.• Post-process /Analysis needs Post-process /Analysis needs • Operating System needs.Operating System needs.• Networking, other hardware needsNetworking, other hardware needs

Software for D.A.SSoftware for D.A.S

• Pascal, BASIC, Pascal, BASIC, C/C/C++, VB, ….etc.C++, VB, ….etc.

• LabTech-Notebook, LabVIEW, LabTech-Notebook, LabVIEW, Agilent-VEE, Genie, DasyLab, …etc.Agilent-VEE, Genie, DasyLab, …etc.

• Issues : – GUI s/w costs? Learning / training?

– Availability of drivers?

– Complete hardware compatibility?

– Real-Time?

– Software overheads on CPU?

• SCADA Software…

Thank you for your Thank you for your Attention.Attention.

Oh……….. the Wait is Oh……….. the Wait is

OVER!!OVER!!