Dmx Testers

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Dmx Testers

This is a guide to explain what they are, the different types available and what they do without going too far into the technical side of how they do what they do.
This guide is just for the 'tool-belt' sized ones and not for the more accurate diagnostic tools such as say a 'microscope' or ' lil' dmxster '

They can be a 5-pin or a 3-pin xlr plug and there are a variety of types available across the whole budget range.

The l.e.d.'s should be showing a 'flicker' to show a good signal as dmx signals send out 'pulses' of information every micro-second.
If the tester you have only shows the l.e.d. as 'on' then this is only a basic tester and not showing the proper signal results.
This is not true in all cases as some equipment sends out dmx signals which appears differently on all testers, though this is rare it is worth mentioning.

They can be used as a basic cable tester to show if there is a break in one of the three cables needed to send the dmx signal.
Also if the dmx is not present at all meaning something is un-plugged somewhere.

Types available - starting with the cheaper options and working to the more expensive lower down the list and therefore the better, more comprehensive testers.

Single l.e.d. type - Not really the best type to use. These have a single coloured led which merely shows the dmx signal is present or not therefore cannot show whether you have lost positive or negative side of the signal just the signal itself. Cheap and very basic type but not good for seeing what's actually wrong with the signal just if it is there or not.
This was a variation of the audio industries line-tester which now seem to be uncommon probably due to audio desks becoming so advanced to allow feedback along the lines?

Two colour l.e.d. - Shows the positive and negative side of the signal is present and can show reversed dmx as well depending on the design of the circuit.

 - There is also the same type which is with just a single bi-coloured l.e.d. though this can be hard to read at times as the red and orange (made of green/red l.e.d.'s both illuminating at the same time) can make it hard to differentiate between the two. This can also be a problem even when other colours are used in the l.e.d.

Three
colour l.e.d. - Normally a standard design of single red, green and yellow l.e.d.'s.
Easy to read as all l.e.d.'s flashing slightly means good, the lack of a single l.e.d. is explained further in the guide supplied (at least with my ones that is)
Shows the positive and negative side of the signal is present, also shows the earth insulation across the signal poles and the refresh rate of the signal.
This makes the tester better for diagnosing problems with equipment such as lighting consoles, controllers and amplifiers (or buffers)
In this way (from using them for a long time) i can tell you when an operator is saving to disk on a hog 2 console for instance as the yellow freezes temporarily.
Red is the positive side of the signal, Green the negative and yellow shows the refresh rate of the signal.
They show the positive and negative sides in reverse dmx as well.
If reversed dmx then the red/green shows the same way meaning good but they are monitoring the opposite side of the signal.
Currently the ones available on ebay and on my website come with a lanyard to hang the tester around your neck, tie to a tool-belt or a harness to make them harder to lose or be stolen!

All the types so far use the signal voltage to power the tester itself and are encased within a standard xlr plug.

Nine l.e.d. type - Also with a mode switch to change the test, you would need to read the manual to understand these fully.
Very easy to read and understand once your used to testing dmx as each l.e.d. shows a different piece of information.
This is one of the easiest to understand as it shows almost everything you would need to know but it is battery powered and these (3 x LR44) batteries are not cheap to buy.
A good point is that they can be plugged in-line as they have a plug and socket on each end (whereas all the others are just a plug).
This also means that it is possible to use them as a double ended cable tester rather than a single ended test using the other types.
These show : if the screen & data line are connected correctly, if Data poles have reversed polarity.
Black Aluminium Housing makes it look pretty too and they come with a leather pouch.
They also have a bright white LED torch built-in (so you can wear out the batteries quicker?).


Summary - The better testers are probably the 3 or 9 l.e.d. types as they show all the faults possible (within their design specifications, there is much more that can be wrong which you would need a much more expensive tester to see fully)
There is quite a price difference between the two though.
The other types are okay as well though they do not show everything the more expensive ones do, but you get what you pay for.

The first of this size i ever saw was the 'terminator' which was a 2x l.e.d. design back in the mid-nineties. These used to cost around £60 then and did not terminate the signal as it might sound.
This then made me see the need to make one rather than buying my own so i made a simple
2x l.e.d. design when i worked for Vari*lite which i then supplied to road-crew coming through our workshop - as well as socapex testers or 'grenades' as they are aften known.
This was mainly because they didn't have time to make their own and i could during my lunch-break.
Later, in my freelance career, with help from a colleague there was the development of a 3 l.e.d. design which i still manufacture to this day (see my auctions for these)
I have made many variations of testers in my time but i still find this one has proved the most popular.

I have tried to keep this as an unbiased guide even though i do sell them on ebay and i hope this answers some of the questions people have about what they are and what they do.

They can also can be known as 'sniffers' by many within the industry, mine are known as 'jamies magic torch' now in the same way as i have made so many over the past 15 years, though it has nothing to do with the classic cartoon!

Feel free to take a look at jamieshurlock as my user id on ebay to see the ones i sell and make your own opinion of them.

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