Drive condition monitoring

1 . A computer-implemented method for condition monitoring of an AC drive, the method comprising:

obtaining an image of a component surface of the AC drive captured by a digital camera fixedly installed in relation to the AC drive, wherein the image includes a first number of pixels;

determining, using the image and at least one reference image for the component surface, a contamination index of the image, wherein the at least one reference image includes the first number of pixels and wherein the at least one reference image is captured by the digital camera fixedly installed in relation to the AC drive before the component surface is exposed to contamination; and

triggering, in response to the contamination index being above a pre-determined first threshold, a maintenance warning.

2 . The computer-implemented method of claim 1 , wherein the obtaining the image comprises receiving the image or retrieving the image from a memory.

3 . The computer-implemented method of claim 1 , further comprising:

illuminating, by a light source, the component surface at least while capturing the image;

capturing, by the digital camera, light reflected from the component surface; and

storing or transmitting the image.

4 . The computer-implemented method of claim 1 , wherein the determining the contamination index of the image comprises:

calculating, per a pixel of the first number of pixels, an absolute value of a deviation of an intensity value of the image from an intensity value of the at least one reference image; and

determining the contamination index by adding together, for the first number of pixels, the absolute values calculated.

5 . The computer-implemented method of claim 1 , wherein the image and the at least one reference image comprise a second number of colour channels, and the determining the contamination index of the image comprises:

calculating, per a colour channel of the second number of colour channels and per a pixel of the first number of pixels, an absolute value of a deviation of an intensity value of the image from an intensity value of the at least one reference image; and

determining the contamination index by adding together, for the first number of pixels and for the second number of colour channels, the absolute values calculated.

6 . A condition monitoring system comprising at least:

a digital camera fixedly installed in relation to an AC drive, the digital camera being configured to capture at least one reference image for a component surface of the AC drive before the component surface is exposed to contamination, wherein the at least one reference image includes a first number of pixels, and further configured to capture an image of the component surface of the AC drive including the first number of pixels;

means for determining, using the image and the at least one reference image for the component surface, a contamination index of the image; and

means for triggering, in response to the contamination index being above a pre-determined first threshold, a maintenance warning.

7 . The condition monitoring system of claim 6 , further comprising:

a light source fixedly installed in relation to the AC drive and configured to illuminate the component surface at least while the digital camera is capturing the image.

8 . The condition monitoring system of claim 7 , wherein the digital camera is configured to capture light reflected from the component surface.

9 . The condition monitoring system of claim 6 , wherein the means for determining the contamination index are further configured to perform:

calculating, per a pixel of the first number of pixels, an absolute value of a deviation of an intensity value of the image from an intensity value of the at least one reference image; and

determining the contamination index by adding together, for the first number of pixels, the absolute values calculated.

10 . The condition monitoring system of claim 6 , wherein the image and the at least one reference image comprise a second number of colour channels, and the means for determining the contamination index are further configured to perform:

calculating, per a colour channel of the second number of colour channels and per a pixel of the first number of pixels, an absolute value of a deviation of an intensity value of the image from an intensity value of the at least one reference image; and

determining the contamination index by adding together, for the first number of pixels and for the second number of colour channels, the absolute values calculated.

11 . An arrangement comprising:

a digital camera configured to, when the digital camera is fixedly installed in relation to an AC drive, capture at least one reference image for a component surface of the AC drive before the component surface is exposed to contamination, wherein the at least one reference image comprises a first number of pixels, and further capture an image of the component surface of the AC drive comprising the first number of pixels;

a processor, and a memory storing instructions that, when executed by the processor, cause the processor to:

determine, using the captured image and the at least one reference image for the component surface, a contamination index; and

trigger, in response to the determined contamination index exceeding a pre-determined threshold, a maintenance warning.

12 . The arrangement of claim 11 , further comprising:

a light source configured to be installed in relation to the digital camera and/or to the AC drive and configured to illuminate the component surface at least while the digital camera is capturing the image.

13 . The arrangement of claim 12 , wherein the digital camera is further configured to capture light reflected from the component surface.

14 . The arrangement of claim 11 , wherein the determining of the contamination index includes:

calculating, per a pixel of the first number of pixels, an absolute value of a deviation of an intensity value of the image from an intensity value of the at least one reference image; and

determining the contamination index by adding together, for the first number of pixels, the absolute values calculated.

15 . The arrangement of claim 11 , wherein the captured image and the at least one reference image each comprise a second number of colour channels, wherein the determining of the contamination index includes:

calculating, per a colour channel of the second number of colour channels and per a pixel of the first number of pixels, an absolute value of a deviation of an intensity value of the image from an intensity value of the at least one reference image; and

determining the contamination index by adding together, for the first number of pixels and for the second number of colour channels, the absolute values calculated.

16 . The arrangement of claim 11 , wherein the digital camera is further configured to capture images of the component surface of the AC drive periodically.