Extending Cable On Ir Lamps

[Alexg]

Hey,

In the instructions for the Dennard DM/880N50-715 it says to not extend the cable from the lamp to the PSU as this will reduce light ouput at the IR lamp, in reality how much of an issue is this?

I want to place the PSU 15m (MAX) from the PSU, I was going to use 2 core 2.5mm cable between the PSU & the lamp, would this be OK?

Thanks.

[ian.cant]

It would be foolish to not adhere to the manufactures recommendations, not only for reasons of operation but for health and safety. Bear in mind should it go tits up and burn something your insurance would be invalid because you didnt follow the manufactures instructions.

Why not move the PSU and run a new supply?

[Guest The Installer]

depending on the psu type that came with the lamp, there may be a pot to adjust the output voltage (under dennards instructions), dennard normally specify no more than 8m as the intensity and life of the bulb is greatly affected.

the above option to move the psu is probably the best option, but if you have to leave it where it is use a silicone based heat resistant cable

can i ask if your using 20w or 50w tungsten halogen lamps?

[WatchdogSecurity]

depending on the psu type that came with the lamp, there may be a pot to adjust the output voltage (under dennards instructions), dennard normally specify no more than 8m as the intensity and life of the bulb is greatly affected.

the above option to move the psu is probably the best option, but if you have to leave it where it is use a silicone based heat resistant cable

can i ask if your using 20w or 50w tungsten halogen lamps?

Dennard say DONT extend the cables under no circumstances, and thats using their OWN PSU/Photocells

[hastings]

Cant you use mains lamps ? or are the others existing ?

[Guest The Installer]

soz, think you may not have understood me properly, some dennard psu's are adjustable to allow longer length of cable, but are set up as standard for upto and not exceeding 8m, give dennard a call, they should be able to inform you wether you have an adjustable supply and give you the correct values to set the output to

they have helped me in the past with lengths over 8m, but only by a short amount

hope this clears up the mess i got myself into

[WatchdogSecurity]

soz, think you may not have understood me properly, some dennard psu's are adjustable to allow longer length of cable, but are set up as standard for upto and not exceeding 8m, give dennard a call, they should be able to inform you wether you have an adjustable supply and give you the correct values to set the output to

they have helped me in the past with lengths over 8m, but only by a short amount

hope this clears up the mess i got myself into

what model of psu can this be done on the 880/883 PSU?

[Doktor Jon]

This type of Infra red illuminator relies on a hot filament bulb being run at or near to it's optimum voltage.

If the voltage is gradually reduced by the internal resistance of the cable being used (i.e. as the cable is lengthened), then there are two specific effects; on the plus side, by under running a bulb it tends to increase its operating life, but on the negative side, the amount of Infra Red light emitted is reduced.

Now depending on the application (in other words the size or distance of area to be illuminated), a slight reduction in IR output may not actually be detrimental, unless every drop of IR output is critical.

In practical terms, a 5% reduction in output (for example) at 715nM, may well be acceptable, whereas a 5% reduction at 830nM may not.

This would be due to the specific sensitivity response for the imager being used. Again as an example, if the camera has 40% sensitivity at 715nM, but only 25% sensitivity at 830nM, then a 5% loss would be far more obvious at the higher frequency.

Ultimately, it really depends on which camera you are using (including light gathering ability of the lens), what frequency IR filter is fitted, and how far you really need to illuminate from the lamp.

[Alexg]

Thanks for the replies,

Hastings:- Mains lamps are a bit too big for this installation, the little microfloord Dennard units are the perfect size.

The Installer:- Thanks, I'll have a look when it comes to see if I can adjust the voltage to compensate

Docktor Jon:- Thanks, I was hoping that by using oversized cable i.e. 2.5mm the voltage drop would be very minimal, the reason I was hoping to extend the cable was so I could do one run of conduit rather than 2, if I need to get mains to the camera head I need to run another length of conduit underneath for the 240v. This is for neatness rather than ease of installation.

The IR lamp is 715nm and it is a very small enclosed area, it's a very low light camera too (0.001 lux) I only need to add 4 meters onto the lamp cable, 4 meters in 2.5mm cable, will this make any difference?

Thanks again guys.

[Doktor Jon]

Hi Alexg,

If you want to do a test using a normal LV bulb and measure the voltage drop with the cable you intend using, I doubt that it's going to be mind numbingly awful.

In the past, I've actually run this type of illuminator for distances of perhaps 20 metres or more (from the supply), sometimes using 12v AC and sometimes using 24Ah 12v lead acid batteries. Mind you, I was using a good IR sensitive camera (@ 830nM), with a fairly compact area being illuminated.

It's not really possible to give absolute assurances without taking account of the camera and lens types, and how they're set up. I tended to use Manual Iris lenses, with the Electronic Iris enabled on the camera. It worked well for me, but others would almost certainly have done it differently.