LabVIEW: Module to Generate Step Increments

What is this Step Increment Generator?

It's a small calculation block that allows you to increment a setting of an instrument a given number of times, with a given step size.

It starts from a given start value.

When it reaches that maximum, it starts counting all over from the start value.

It's Counter input is typically a loop counter.

When it reaches the upper limit, it sets a Finished flag. You can use that value in your downstream flow to stop looping.

Example

In the example below, I use this block two times.

One time in the lower section (outer loop) to make a power supply loop between 8 V and 14V. Without exit. This one keeps looping forever.

The other timer in the top section (inner loop) makes a DC load loop between 0 A and 7.8 A. With exit. Once the upper limit is reached the loop breaks and returns to the outer loop.

Here's the block diagram of the outer and inner loop of that process. The two Increment Generators are highlighted.

You can see that in the outer block the Finished flag isn't used. This loop keeps running until an operator presses the Stop button.

In the inner loop, the Finished flag is used to end the loop's execution and exit back to the surrounding block.

Why?

Step increments within a given range are often used to measure the behaviour of a component or circuit.

You step to the next measurement point and collect the data.

This is a way to fully automate measurements on a device and log the measurements to a file.

The example above is part of an efficiency logger for a dc to dc converter.

Here's output data, and a graph based on such measurements.

Each line in the diagram above represents 1028 test setups. From 0 V - 0 A to 14 V -7.8 A. On each step you need to measure the power at input and the power delivered by the device under test, to measure efficiency. This type of characterisation, where you need a lot of manual effort to set up and write down measure points - repetitive - is where I think that automatisation becomes more efficient. I don't know where the magic border between doing everything manual, and learning + building automation, becomes obvious. It depends on who pays you and what type of activities you want to do on your job. Anyhow, once you spend the time learning automation, that border drops. You spend less time automating your setup. From my own experience, learning to control an instrument and learning the basics of LabVIEW took a few months. Then, automating a process took a few weeks. Now I'm able to automate a test setup - including detailed logging to excel,  in a day, given that I know the instruments and the test process.My progress from purchasing LabVIEW up to achieving that skill is documented here on element14. You can trace back from my very first baby steps.

But what's the point? Why make a module for such a small piece of logic as a step increment generator?

In my case, two reasons:

• it's reusable and used multiple times in a single diagram. As an extra, the block's icon uses less space on the main diagram than the separate blocks - leaving more real estate for the flow.
• I always get this wrong at the border conditions (yes: every time). Having it correct and debugged and tested saves me peace of mind.

The Increment Generator for LabVIEW is attached to this blog post.