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Limit Testing

You can use limit testing to monitor a waveform and determine if it always satisfies a set of conditions, usually upper and lower limits. The region bounded by the specified limits is a mask. The result of a limit or mask test is generally a pass or fail.

Setting Up an Automated Test System

You can use the same method to create and control many different automated test systems. Complete the following basic steps to set up an automated test system for limit mask testing.

1.Configure the measurement by specifying arbitrary upper and lower limits. This defines your mask or region of interest.

2.Acquire data using a DAQ device.

3.Monitor the data to make sure it always falls within the specified mask.

4.Log the Pass/Fail results from step 3 to a file or visually inspect the input data and the points that fall outside the mask.

Repeat steps 2 through 4 to continue limit mask testing.

The following sections examine steps 1 and 3 in further detail. Assume that the signal to be monitored starts at x = x0 and all the data points are evenly spaced. The spacing between each point is denoted by dx.

Specifying a Limit

Limits are classified into two types: continuous limits and segmented limits, as shown in Figure 15-1. The top graph in Figure 15-1 shows a continuous limit. A continuous limit is specified using a set of x and y points {{x1,x2, x3, …}, {y1, y2, y3, …}}. Completing step 1 creates a limit with the first point at x0 and all other points at an uniform spacing of dx (x0 + dx, x0 + 2dx, …). This is done through a linear interpolation of the x and y values that define the limit. In Figure 15-1, black dots represent the points at which the limit is defined and the solid line represents the limit you create. Creating the limit in step 1 reduces test times in step 3. If the