Back to Working with Inclination Data
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.