Back to Working with Inclination Data

Calibration

The inclinometer in the crawler is extremely sensitive to changes in attitude of the smallest amount. It is a solid state device that outputs an electrical signal that we can interpret and measure and as a direct result of its extreme sensitivity, it is prone to drift.

It is because of this that to get the best and most accurate results from an inclinometer, the equipment must be calibrated regularly by recognised service agents and under extreme cases also on the day of the inclination test.

It is not uncommon for the calibration of inclinometers to be bad, and to consider the consequences - imagine that the inclinometer is under-reading by a value of 3%, so in other words it is reading a value of -3% when it is on a perfectly flat surface (should be zero of course).

Then we do an upstream inclination test on a drain that is perfectly straight and has a gradient of -1% (i.e. it falls at a rate of 1% from the upstream end).

So, we do the inclination test upstream, so we expect the attitude values to be nice and positive at 1% because the camera is travelling in an upwards direction, but the under read of -3% means that we are recording values of -2% all the way up the pipe.

The result is that the graph may be very difficult to interpret and may even look like it is going the wrong way. There is no surprise in this because that is the data that WinCan VX has received from the camera and the data does not lie.

This is a common issue with customer’s inclination reports when they call our support teams and complain the the graph ‘looks wrong’.

So how do we calibrate the equipment?

Given the extreme sensitivity of the inclinometer, it should be recalibrated regularly, even after the operator has changed the wheels on the camera for a different pipe size because the wheels are likely to be worn by uneven amounts so the camera body will no longer be at the same attitude on a flat surface than it was before the wheel change.

As described previously, the equipment should be calibrated by a recognised service centre for the equipment as prescribed by the manufacturer, but even if this was done maybe 3 months ago, you must not assume that the inclinometer is still in adequate calibration because it has most likely drifted off centre during normal CCTV inspection use.

Some contractors use digital levelling tables which are expensive but offer a rigid metal plate that can be set via controls to any minor angle or dead flat. Then, we can put the camera on the table with its wheels on and set the zero point of the unit in the OSD controls of WinCan VX.

But what about regular TV trucks doing regular work on site?

So you don’t have access to a levelling table and the boss has asked you to do an inclination test and you want to make sure that the calibration is as good as possible. With a little thought and preparation at the office before going to site, this is not hard to do.

The trick is to manufacture some kind of rigid and flat board with 3 points of contact which you can lay on the ground at the back of the truck and then adjust the 3 feet until it is perfectly level in the two 90 degree directions across and along the plate by using a spirit level. This can be a cast steel plate with adjustable threaded feet or a thick flat piece of wood with folded pieces of paper under the 3 contact points. One is more simple than the other, but both will work equally as well.

Once you have the plate flat, you can set the camera up with the correct wheels and place it on the plate and hit the calibration button in WinCan VX OSD controls. This resets the zero point of the unit and now it is ready to complete a test with confidence.

If you go this far and you can setup with cable rollers in the manhole nearest to the truck, then you are already a very long way towards excellent output results from the data.