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Steve Peregrine BEng Hons, Senior Technical Manager

Contents

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Sections

Introduction

This document is designed to offer some insight into drainage inclination testing equipment, explain some of the logic that is considered inside the WinCan VX application, help readers to understand the output reports and assist with diagnosing problems.

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• Attitude - is the angle of slope of the device at any point during the inclination test.

• Altitude - is the height of the device at any given point during the test measured from a specified datum.

• Gradient - is the slope of the pipe or the inclination test represented as a percentage where 0% is dead flat, -1% is a drop of 1m over 100m length in the direction of flow (i.e. a good drain, a happy drain), +1% is a rise of 1m over 100m length (i.e. an unhappy drain) and -100% is a gradient of 45 degrees or 100m drop in 100m length.

• Delta Height - is the change in height either along the entire length of the pipe, the length of the inclination test or between two measurement points with the test. As with Gradient, negative values refer to a drop in height in the direction of flow and positive values describe a rise in height.

Test Options

An inclination test on a pipe can be carried out any one of 4 styles, where the choice of style that will give the best results is largely dependent on the equipment:

• From the upstream end driving forwards away from the truck to the downstream end (i.e. Downstream CCTV inspection direction and Forwards inclination measurement direction).

• From the upstream end driving backwards towards the truck to the downstream end (i.e. Downstream CCTV inspection direction and Backwards inclination measurement direction).

• From the downstream end driving forwards away from the truck to the upstream end (i.e. Upstream CCTV inspection direction and Forwards inclination measurement direction).

• From the downstream end driving backwards towards the truck to the upstream end (i.e. Upstream CCTV inspection direction and Backwards inclination measurement direction).

Remember that only 2 measurements are recorded from the camera during the test, the attitude and the distance. The most significant decision regarding the accuracy of the distance measurement is usually defined by whether or not the camera has a manual winding cable drum or an auto-winding cable drum.

Why? Because if the cable drum rewind is manual and you try to do a Backwards inclination test, you will be relying on the operator at the back of the CCTV truck to pull the cable extremely smoothly and consistently while also winding the handle, which is extremely difficult when you have a drain that is 100m long, almost impossible. So, in this case, it makes sense to do the test forwards so that the drive of the camera pulls the cable and the distances measurements are smooth and consistent.

But, if you have an auto-winding cable drum, then you can do the test backwards with confidence because the machine will pull the cable at a constant rate and without allowing the cable to become tangled with the camera wheels and without any sudden tugs from the operator that can jolt the camera and give bad attitude data points.

In general, backwards inclination tests give better results than forwards where the equipment allows because there is much less effect on the camera unit from the cable.

It is common to see some bad and extremely high or low data points near to the end of the test that is closest to the truck (so at the beginning of the test if the test direction is forwards or at the end of the test if it is backwards). This is because when the camera is close to the inserting manhole, it is common for the cable to be vertical or sloping up towards the CCTV truck, and this force on the back of the camera can have a serious effect on the attitude values, so for the absolute best results, a low manhole roller should be used for the camera cable so that the cable is always directly behind the camera.

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.

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