自动测试设备的预算-Automatic Test Equip

文章摘要：Software that controls this bus is available off the shelf or can be developed in-house. National Instrument's Labview and Agilent's (formerly Hewlett-Packard's) Agilent-VEE are two of the most popular software packages for controlling instruments via the IEEE-488 bus. Alternatively, con

自动测试设备的预算-Automatic Test Equip,标签：计算机控制技术,工厂电气控制技术,http://www.88dzw.com

Software that controls this bus is available off the shelf or can be developed in-house. National Instrument's Labview and Agilent's (formerly Hewlett-Packard's) Agilent-VEE are two of the most popular software packages for controlling instruments via the IEEE-488 bus. Alternatively, control software can be developed using traditional "C" programming, given a certain level of expertise. However, use of the Labview or HP-VEE allows a novice programmer to design sophisticated programs quickly and easily. Labview and HP-VEE come with software modules for driving many common instruments.

A few problems are associated with the use of the IEEE-488 bus. Because the IEEE-488 bus is not standard equipment on most PCs, an interface adapter card must be added, and these cards cost $500 or more. These interface cards are available from companies such as National Instruments, IOTech, Measurement Computing, Agilent, and Tektronix. Added to the cost of this card is the cost of IEEE-488 cables, which are about $20 each. The IEEE-488 instruments themselves are expensive. Also, if your test system requires that you develop custom instruments, significant software and hardware development time will be necessary. A custom instrument requires a microprocessor and an IEEE-488 interface controller, both of which imply substantial development time.

Figure 5 depicts the MAX145X tester, a key portion of the pressure-sensor test system shown in Figure 4. This tester is a multiplexer/driver instrument developed by Maxim. Using an oven, a pressure controller, and the multiplexer/driver instrument, original equipment manufacturers (OEMs) that purchase the MAX1457, MAX1458, or MAX1459 pressure-sensor signal-conditioning chip can easily test and calibrate these ICs. This tester calibrates and tests these signal-conditioning chips when they are used in conjunction with pressure sensors. Because this system allows access to the Labview program that controls the IEEE-488 bus, the test system can be readily modified to meet the unique needs of a particular production line. Simple text commands sent to the tester communicate with the MAX1457-MAX1459 and apply the compensation algorithm that compensates the accompanying pressure sensors.


Figure 5. This simplified block diagram of the tester portion of the Figure 4 test system shows the custom hardware developed to test and compensate pressure sensors mated with MAX1457-MAX1459 signal-conditioning ICs.

Test-System Design Techniques

Hardware Design

Controlling test instruments using an IEEE-488 bus may require the time-consuming process of writing software that controls the interface. You can save software development time, however, by using a bus-controller IC such as National Instrument's NAT9914. Using a bus controller also frees the microprocessor from the time-consuming activity of monitoring the IEEE-488 bus.

When noise levels or measurement precision is critical, addressing these concerns from the beginning is important. Such performance problems become increasingly difficult to solve as the project progresses. In the tester pictured in Figure 5, two precautions were taken to achieve the desired measurement accuracy. First, the digital and analog grounds were kept separate. Second, high-speed optocouplers were used to isolate microprocessor-switching noise from the analog signals.

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