Hum Bars!

[lowlofe]

Evening

I have a Vantage B&W camera that has started spitting up hum bars at night

The image is clear during the day but as soon as it starts to get dark the hum bars are appearing and start jumping up and down :/

I have another camera exactly the same on the other side of the building (Dennard 2010 housing) and its working correctly.

Just wondering if anyone can shed some light on the matter?

Many thanks

alex

[Doktor Jon]

lowlofe,

If you're convinced that the problem does not occur during the day ( may not be quite so obvious, but still faintly present in the image ) you need to have a think about what's changing at night; Security lighting, IR lamps, housing heaters, something else on the same power circuit operating on a timer or photocell activation.

If you check the image coming straight out of the camera and the problem is visible on a test monitor, look carefully at possible problems with the power supply. If it is not present at the camera but appears at the monitoring end (i.e. camera lead plugged straight into monitors Video In), you can quickly confirm if it's an earth loop hum by temporarily disconnecting the earth lead inside the monitors mains plug (assuming it has one fitted). If the problem disappears then it is an earth loop hum.

This is just a quick test and once you've done it, reconnect the earth lead.

Depending on what is causing the hum bars, and the voltage supply of your camera, then there are a number of possible options for getting rid of the problem.

Perhaps do some quick tests and let us know how you get on ....

[lowlofe]

Doktor Jon.

They are only there once it gets dark i know this for sure as they are pitch black :/

The housing has got the standard dennard heater in it... but so does 15 odd other cameras on site and there working fine.

That housing has a sanyo transformer in it, again 4 of the other cameras have the transformers in the housings but they have been there since the dorn of time and haven't had any problem with the others.

Will do some tests when i get back on site tomorrow

Regards

alex

[ICEbear]

Doktor Jon.

They are only there once it gets dark i know this for sure as they are pitch black :/

The housing has got the standard dennard heater in it... but so does 15 odd other cameras on site and there working fine.

That housing has a sanyo transformer in it, again 4 of the other cameras have the transformers in the housings but they have been there since the dorn of time and haven't had any problem with the others.

Will do some tests when i get back on site tomorrow

Regards

alex

hi alex,

"sanyo transformer" is this a (pulse width switch mode power supply) or a wire wound transformer with bridge-rec/smoothing-caps/regulator ?

is the transformer just running the heater or camera as well ?

I'll throe some idears at you:

if its switch mode, change every capacitor on the HT side (including the big one) wont cost much (

[lowlofe]

I have tried another transformer and its not that.

The heater in the housing is 240vac, Disconnected the power to that and that didnt fix the problem

I took a feed direct from the camera into a test monitor and it still had the lines

All in pitch black and the freezing cold up a ladder :/

Something is telling me that its the camera itself to blame, Looking at them they do look a little old.

Regards

alex

[sjonley]

Personally I would swap the camera with hum bars at night for a camera without hum bars at night and see if the problem follows the camera.

The hum bars occur usually when their is a potential difference between the camera and monitoring equipment and hence a current usually flows down the sheath or brading of the coax. Sometimes isolating the housing if mounted on a metal structure or using a ground isolation transformer such as our GLI001 (

[ICEbear]

ground isolation transformer, yes stuart good advice, i forgot about them, the good old humbuggs also known as ground-loop isolators, yes,yes,yes.

if is'nt that, swop the camera

up ladders in this cold weather

[ICEbear]

ive never liked the idear of camera housing at 240vac, theres no need when 24v will do everything, can you imagin a little error at the top of a ladder

[sjonley]

i know what mains feels like having dropped a screwdriver across some main terminals once. talk about bad hair day!

[Doktor Jon]

Doktor Jon.

They are only there once it gets dark i know this for sure as they are pitch black :/

The housing has got the standard dennard heater in it... but so does 15 odd other cameras on site and there working fine.

That housing has a sanyo transformer in it, again 4 of the other cameras have the transformers in the housings but they have been there since the dorn of time and haven't had any problem with the others.

Will do some tests when i get back on site tomorrow

Regards

alex

If the camera is 12vDC and it's powered from a Sanyo unregulated supply (the transformer), I'd be tempted to take the camera down and test it on a bench with a new power supply unit. It could well be a problem with the camera or the PSU, although I'm leaning away from it being an Earth Loop Hum (I'm not saying it definitely isn't, but that's dropping down my list of possibles).

If it is a 12v DC camera, you can easily isolate that from the housing to ensure it's not Earth Loop Hum, but my giblets are pulling me towards an age related (component issue) camera induced problem. It will be interesting to see what your tests throw up.