Advantech PCI-1710UL Bedienungsanleitung PDF herunterladen (Seite 2)

Data Acquisition Boards

Analog Outputs (D/A)

The opposite of analog to digital conversion is digital to analog (D/A) conversion. This

operation converts digital information into analog voltage or current. D/A devices allow

a computer to control real-world events.

Analog output signals may directly control process equipment. The process can give

feedback in the form of analog input signals. This is referred to as a closed loop control

system with PID control. Analog outputs can also be used to generate waveforms. In this

case, the device behaves as a function generator.

Digital Inputs and Outputs

Digital input/output functions are useful in applications such as contact closure and switch

status monitoring, industrial On/Off control and digital communications.

Counter/Timer

A counter/timer can be used for event counting, ﬂowmeter monitoring, frequency counting,

pulse width measurement, time period measurement, and so on.

Getting Started

Advantech: The Source For What You Need

Advantech manufactures data acquisition hardware and software for measurement,

monitoring and applications control. The following guide is provided to help you choose

components for your data acquisition system.

Step 1: Know Your Fundamental Goal

Decide whether your DAQ system will be used primarily for measurement, monitoring,

control, or analysis. Know the data requirements of your process, and know the number

of data collection points in your system. Know the required data collection speed, the

sampling rate, the type of measurement, the voltage or current being produced, the desired

accuracy and the output resolution at each data collection point. Finally, know the timing

of events in your system, and any special environmental conditions that exist.

Step 2: Hardware Selection

Select the hardware required to achieve your fundamental goal. Advantech provides plug-in

boards for Analog-to-Digital, Digital-to-Analog, Digital I/O needs. Both ISA and PCI bus

products are available. Your hardware selection should be based on ﬁve major criteria:

1. Number and types of channels

2. Differential or single-ended inputs

3. Resolution

4. Speed

5. Software compatibility with hardware

Step 3: Accessory Selection

Most applications require additional accessories which are available as separate items.

These include:

1. Expansion peripherals to add channels to your system

2. Cables, signal conditioners and external boxes such as screw terminals or BNC

accessories

Step 4: Software Selection

More than any other single factor, software will determine your system start-up time, as

well as its effectiveness, suitability for your application, and ease of modiﬁcation.

Three major criteria should determine the choice of software:

1. Operating system used

2. User programming expertise

3. Software compatibility with hardware

Data Acquisition and Control

Tutorial & Software

PC-based Data Acquisition (DAQ)

System Overview

Because industrial PC I/O interface products have become increasingly reliable, accurate,

and affordable in the last few years, PC-based data acquisition and control systems are

nowadays widely used in industrial and laboratory applications such as monitoring,

control, data acquisition and automated testing.

It requires know-how of electrical and computer engineering to select and build a data

acquisition (DAQ) and control system that actually does what you want. This tutorial

gives a brief introduction to what data acquisition and control systems do and how to

conﬁgure them. Here, we cover:

 Transducers and Actuators

 Signal Conditioning

 Data Acquisition and Control Hardware

 Getting Started

Transducers and Actuators

A transducer converts temperature, pressure, level, length, position, etc. into voltage,

current, frequency, pulses or other signals.

Thermocouples, thermistors and resistance temperature detectors (RTDs) are common

transducers for temperature measurements. Other types of transducers include ﬂow

sensors, pressure sensors, strain gauges, load cells and LVDTs, which measure ﬂow

rate, pressure variances, force or displacement.

An actuator is a device that activates process control equipment by using pneumatic,

hydraulic or electrical power. For example, a valve actuator can open and close a valve

to control ﬂuid rates.

Signal Conditioning

Signal conditioning circuits improve the quality of signals generated by transducers before

they are converted into digital signals by the PC's data-acquisition hardware. Examples

of signal conditioning are signal scaling, ampliﬁcation, linearization, cold-junction

compensation, ﬁltering, attenuation, excitation, common-mode rejection, and so on.

One of the most common signal conditioning functions is ampliﬁcation. For maximum

resolution, the voltage range of the input signals should be approximately equal to the

maximum input range of the A/D converter. Ampliﬁcation expands the range of the

transducer signals so that they match the input range of the A/D converter. For example,

a x10 ampliﬁer maps transducer signals that range from 0 to 1 V into the range 0 to 10

V before they go into the A/D converter.

Data Acquisition & Control Hardware

Data acquisition and control hardware generally performs one or more of the following

functions: analog input, analog output, digital input, digital output and counter/timer

functions. This section will discuss each function and list some considerations that are

important when you select a data acquisition and control system.

Analog Inputs (A/D)

Analog to digital (A/D) conversion changes analog voltage or current levels into digital

information. The conversion is necessary to enable a computer to process or store the

signals.

The most signiﬁcant criteria when selecting A/D hardware are:

1. Number of input channels

2. Single-ended or differential input signals

3. Sampling rate (in samples per second)

4. Resolution (usually measured in bits of resolution)

5. Input range (speciﬁed in full-scale volts)

6. Noise and nonlinearity

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