There are different types of ignitors depending on the lamp to be started, and the same lamp can even be started with different models of ignitor.
There are dependent or semi-parallel ignitors (which are connected to an intermediate ballast input, also called pulse transformers, because this is what is actually obtained at the ballast output: an increase and transformation of pulses generated by the ignitor on a part of its coil).
The “dependent” classification refers to a type of ignitor that depends on the ballast, i.e. it cannot endure long enough on its own to start the lamp. Once the lamp has been started, no lamp current passes through them. Dependent ignitors are widely used with high pressure Sodium lamps. They are also used for some Halide outputs.
On the other hand, so-called independent or series (or superimposed) ignitors, can endure long enough to start the lamp. They are not tapped into the ballast at any intermediate point on its coil, but are instead serially connected to the ballast and connected in parallel to the lamp. Consequently, they withstand the passage of the current that feeds the lamp when operating. Independent ignitors are suitable for high pressure Sodium and Metal Halide lamps.
Independent (or parallel) two-wire ignitors are a third type of ignitor. This type of ignitor supplies a lower voltage (from 800V to 1200V), albeit independently of the ballast. It is connected in parallel to the lamp, but also fails to withstand the passage of its current.
As far the possibility of fitting them at a distance from the lamp is concerned, the dependent types normally ensure switch-on at a distance of 20m, whereas our independent ones only allow for a distance of 2m to 3m, given that switch-on cannot be ensured at longer distances. Finally, parallel ignitors do not lose pulse with increases of distance, as they provide much greater energy (these ignitors take greater load capacity).
This behaviour with respect to distance is caused by a particular feature of the connection cables between the ignitor and the lamp and those of the ignitor itself. It is defined as the load loss capacity per metre of cable and the ignitor’s load loss capacity.
Pulse frequency in dependent and independent ignitors is usually high, more so in the latter than in the former. The capacity of the cables between them, as a result of placing together two conduction wires between insulators, and even between the individual wires and the conduit pipe, gives rise to the pulses generated by it reaching the lamp with a greatly reduced amplitude value, and if the distance is greater than the recommended limits, the lamp will not be able to start.
An ignitor’s load capacity is given in the technical features section in the manufacturer’s catalogue. The load capacity of the cables will be given by their manufacturers, but for guideline purposes, it is a good idea to assume a capacity of 20 to 50 pF/m for single core cable and from 70 to 150 pF/m for multicore cables. In order to ensure switch-on by an ignitor, the product of multiplying the metres per capacity by cable metres must be lower than the load loss capacity that characterises the ignitor.
ELT Ignitors: http://www.elt.es/productos/i-arrancadores_m.html?0&3
Technical information and distance according to lamps: http://www.elt.es/productos/pdf/380000000.pdf
Juan José Banegas