EP2198672A1

EP2198672A1 - Method for determining operational parameters for a gas discharge lamp to be operated with electronic ballast and corresponding ballast

Info

Publication number: EP2198672A1
Application number: EP08802680A
Authority: EP
Inventors: Dirk Dworatzek; Andreas HÖGL; Andre Mitterbacher
Original assignee: Tridonicatco GmbH and Co KG
Current assignee: Tridonic GmbH and Co KG
Priority date: 2007-10-02
Filing date: 2008-09-26
Publication date: 2010-06-23
Anticipated expiration: 2028-09-26
Also published as: WO2009046891A1; ATE523065T1; CN101816219B; CN101816219A; EP2198672B1; DE112008002296A5

Abstract

In order to determine operational parameters of a gas discharge lamp (L) to be operated with an electronic ballast (V), the cold resistance (Tcold) and the hot resistance (Rhot) of a helix (W1) are determined at at least two different times during the preheating phase. During the preheating phase, the heating power or the heating current is kept constant or alternatively, a predetermined heating power or a predetermined heating current is set at the beginning of the preheating phase. Thus a split of the resistance values during the preheating phase is carried out. The differential resistance (Rdiff) is formed from the hot resistance (Rhot) and the cold resistance (Rcold) and is independent from the start temperature of the helix (W1). The differential resistance (Rdiff) is compared to stored reference values in order to set the operational parameters corresponding to the lamp type on the ballast (V).

Description

METHOD FOR DETERMINING OPERATING PARAMETERS OF A MIT

A GAS DISCHARGE LAMP TO BE OPERATED ON AN ELECTRONIC BALLAST AND A CORRESPONDING BALLAST

The invention relates to a method for determining operating parameters of a gas discharge lamp to be operated with an electronic ballast.

Such a method is known from EP 1519638 Al. In this known method, the voltage drop across a resistor located on the primary side of the heating transformer is measured at two different times during the preheating phase. The two voltage values thus determined are compared with reference voltage values stored in a memory to determine the lamp type.

According to EP 1125477 B1, it is known to determine the filament resistance of the lamp in order to determine the lamp type by comparison with a reference resistance value stored in a register.

The invention has for its object to find a solution to the above problem.

Starting from the input described known method (EP 1519638 Al), the solution consists in the combination of the features specified in the characterizing part of claim 1. The invention has for its object to provide a simple method for detecting the lamp type, which improves the detection reliability compared to the previously known methods.

The object is achieved according to the invention by the sequence of the following process steps: a) adjusting the helical current flowing through at least one heating coil so that it has a predetermined current intensity, b) measuring the filament voltage directly or indirectly, c) determining the lamp type, if necessary after calculation of the filament resistance - based on the measured filament voltage by comparing the measured filament voltage or the calculated filament resistance with corresponding standard values, which are stored for each lamp type in a table.

The solution according to the invention adopts the principle of resistance measurement, preferably at heating power held constant during the preheating time or at constant heating current, and uses the difference value (distance) from hot and cold resistance instead of the hot resistances to determine the lamp type.

But it is also sufficient that at the beginning of the preheating a certain heating power or a certain heating current is set. This can be done via the specification of a corresponding operating frequency and a corresponding switch-on time or a corresponding duty cycle. If the heating circuit is designed with a power source or current source characteristic, it can be ensured that during the preheating phase, the heating power or the Heating current sets in a certain window, which remains within a certain range of values.

The prior art has always used heating topologies or control methods with a voltage source characteristic or voltage regulation, which are far less suitable for the method operated here.

The invention is based on the following finding: The measurement of the helical resistance via the helical current and the helical voltage presupposes that an electrical power is supplied to the helix. This leads to the heating of the coil. Since the coils are usually made of metal, their resistance increases with temperature. The spiral temperature depends on the heating power supplied to the coil. In qualitative terms, this means that the higher the supplied heating power, the higher the coil resistance. It is now assumed that a second lamp type differs from a first lamp type in that the

Coil resistance of the second lamp type is twice as large as that of the first lamp type. If now - as previously for measuring the helical resistance a previously known

(impressed) filament voltage is applied to the filament, so the filament of the second lamp type supplied heating power (P = U ² / 2R) - because of the double filament resistance - only half as large as the filament of the first lamp type supplied heating power (P = U ² / R). As a result, the filament of the second type of lamp is heated less than that of the first type of lamp. The thermal resistance increase of the filament of the second lamp type is thus smaller than that of the filament of the first type of lamp. The thermal resistance increase thus counteracts the increase in the coil base resistance, with the result is that the detection reliability of the lamp type is reduced.

Now, if the coil according to the invention a predetermined (impressed) current is supplied, and then if the coil resistance is determined by measuring the filament voltage, the tendency is exactly the opposite. In this case, the heating power supplied to the coil of the second lamp type (P = I ² * 2R) is twice as high as the heating power supplied to the coil of the first lamp type (P = I ² R), with the result that the thermal resistance increase of the Spiral of the second lamp type is higher than the thermal resistance increase of the filament of the first lamp type. As a result, the thermal resistance enhancement enhances the effect of increasing the coil base resistance, with the result that the detection reliability of the lamp type becomes remarkable.

In other words, this means that high-impedance coils are even higher impedance when using a power source and the resulting stronger heating over low-resistance coils. This leads to a larger difference of the resistances and thus to an improved recognizability.

In practice, the realization of a power source for filament heating is difficult. Adjusting the helical current flowing through at least one heating coil to have a predetermined current intensity is therefore best realized by adjusting the helical current.

According to a development of the method according to the invention, a further step can be added to the above-mentioned method steps, namely: Setting at least one operating parameter for the determined lamp type.

The formation of the differential resistance has the advantage that the influence of the starting temperature for measuring the cold resistance is eliminated.

Further developments of the method according to the invention are the subject of claims dependent on claim 1.

The invention further relates to a ballast for at least one gas discharge lamp, with which the inventive method can be performed. This ballast is characterized by the features of claims 12 and 13. Further developments are the subject of claims dependent on the claims 12 and 13 claims.

The invention further relates to a ballast for a gas discharge lamp, which operates according to the method described above. This ballast has the following features:

Storage means for a table, in which for each lamp type for a certain filament current intensity the corresponding filament voltage or the corresponding filament resistance is stored,

- Stromeinstellmittel, by means of which for at least one heating coil, a predetermined helical current is adjustable,

Measuring means for directly or indirectly measuring the voltage drop across the heating coil charged with the predetermined filament current,

if appropriate, means for calculating the filament resistance by quotient formation from the measured filament voltage and the set filament current, Comparative means for determining the lamp type by comparing the measured filament voltage or the calculated filament resistance with the corresponding value set down in the table.

For adjusting the filament current, the current setting means may comprise a control part for the filament current. A refinement of the ballast may consist in providing means for setting at least one operating parameter for the determined lamp type.

The measuring means may comprise a voltage divider connected in parallel with the filament, from which a signal corresponding to the filament voltage is derived.

To the control part may include a connected in series with the heating coil measuring resistor, from which a measurement signal is derived, which corresponds to the helical current.

Embodiments of the invention will be described below with reference to the drawings.

Show it:

Fig. 1 is a schematic block diagram of the ballast according to the invention;

Fig. 2 is a flow chart showing how the method of the invention is practiced;

Fig. 3 is a graphical representation of the dependence of the helical resistance of the preheating time for three different lamp types and resulting three ranges of variation for the differential resistance of each of these three lamp types;

4 a the dependence of the helical resistance of the

Filament tension with impressed filament tension; Fig. 4 b shows the dependence of the helical resistance of

Filament current with impressed filament current; 5 shows a gas discharge lamp with associated ballast;

Fig. 6 of the block coil voltage generation of Fig. 5 in concrete embodiment.

The ballast V shown in Fig. 1 is used to operate a gas discharge lamp L with two heating coils Wl and W2.

To generate the operating voltage for the lamp L is rectified by a rectifier 1, the mains voltage and smoothed in a smoothing circuit. An inverter 3 generates an alternating voltage which is fed to a series resonant circuit 4. The voltage drop across the capacitor of the series resonant circuit 4 is supplied to the lamp L as the operating voltage.

A programmer 14 connected to a bus determines the start of a preheat phase for the lamp L. He gives to the block 8 a start signal. The block 8 generates the heating power or the filament current for the filaments Wl and W2 of the lamp L. The heating power or the filament current are kept constant during the preheating phase. The heating power or the filament current are led to the lamp L via a block 6, which contains means for limiting the filament voltage. A limitation of the filament voltage is required, for example, a transverse discharge between the individual sections of the heating coils to avoid. The filament current flowing through the "cold" filament W2 generates a voltage drop across the resistor R3, which is conducted to the filament current measuring means 7. At a voltage divider Rl, R2, a voltage is further removed, which is a measure of the filament voltage at the "cold" coil W2. This is the Wendelspannungs- measuring means 9 supplied.

The measurement values continuously measured by the filament current measuring means 7 and the filament voltage measuring means 9 are fed to a memory 15. The memory 15 is controlled by the programmer 14 such that the measured values for the filament current and the filament voltage are stored at two successive times during the preheating phase. The stored measured values for the filament current and the filament voltage are fed from the memory 15 from a quotient former 10, which calculates therefrom the cold resistance and the hot resistance of the filament. These values are forwarded by the quotient generator 10 to the difference value generator 11, which calculates the differential resistance therefrom.

The difference value generator 11 supplies the differential resistance to a decision logic 13, which in turn corresponds to a memory 12 by storing a table for reference differential resistances. The decision logic 13 compares the differential resistance calculated in the block 11 with the reference values in the table stored in the memory 12 and determines the type of the lamp L operated by the ballast V. The determined lamp type is reported by the decision logic 13 to the operating parameter setting means 5, the next other operating parameters, among other things, the heating current or adjust the heating power, if the lamp L is of a different type than the previously operated with the ballast V lamp.

It should be noted in this context that the individual blocks in Fig. 1 need not necessarily be realized by hardware. Rather, it is also possible that the function of some blocks is realized by a corresponding software in a processor. The block diagram in Fig. 1 is intended only for better understanding.

The logical sequence of the individual method steps for determining the lamp type, ie the software representation of the invention, is shown in FIG. This will be explained below.

The illustration in Fig. 2 relates to the case that two lamps are operated in parallel with a ballast. Of course, it also includes the possibility of working with only one lamp.

At the beginning of the preheating phase, the cold resistances Rcoldl and Rcold2 are measured by the two lamps. From the two measured values the absolute value of the

Difference | Rdiff | calculated. Then three cases are distinguished. If | Rdiff | smaller than a first

Reference value is Refl, this means that the two lamps are of the same type. It then goes on in the

"Case 1".

If IRdiffl is greater than the first reference value Refl but smaller than a second reference value Ref2, then means that the lamps are ready, but not of the same type. In this case, the path "Case 2" is taken.

It should be noted at this point that detection of the lamp type can be skipped by checking the coil resistances for certain events. Thus the measurement can be omitted under the following special conditions and an accelerated lamp start can be initiated under the data already stored in the TOE (the operating parameters set after the previous lamp start):

Mains reset or emergency lighting operation. A mains reset is a brief interruption of the mains supply or a brief drop in the mains voltage, which results in a shutdown and a subsequent restart of the electronic ballast. Such a case can be caused by switching the network (by the utility) or by disturbances in the network. An emergency lighting operation may e.g. in the event of mains voltage failure, switching on a (buffered) DC and AC supply voltage or switching to battery operation.

Now, the path "Case 1" should be continued, so that the further evaluation is carried out with the lamp having the lower cold resistance Rcoldl or Rcold2.

It is understood that this point in the flowchart also comes when only one lamp is present. In this case, the splitting of the cold resistances in two paths is eliminated. The further course of the Flowchart is anyway limited to only one coil, be it with the lower cold resistance or the only existing lamp.

Furthermore, it is now checked whether the differential resistance Rdiff is smaller than a predefined substitution resistance value Rsub. This comparison is to check whether the lamp is replaced for test purposes by a so-called substitution resistance, which shows no temperature-dependent resistance due to the thermal conditions. If this is the case, the cold resistance and the hot resistance do not differ. Therefore, if the decision is "Yes", the differential resistance Rdiff is set equal to the hot resistance Rhot.

When the differential resistance Rdiff is greater than the substitution resistance value Rsub, d. h., if - because a lamp is inserted - Rcold and Rhot differ sufficiently, then the result of the decision is "no".

Next, the decision is whether the differential resistance Rdiff is smaller than a first stored resistance value "Level 1". If difference resistance Rdiff is less than this level 1, then the decision is made that this is the lamp type 1.

If the difference resistance Rdiff is between the already mentioned level 1 and a further higher level 2, the decision is made that a lamp type 2 is present. If the difference resistance Rdiff is between the level 2 and another level 3, the decision is made that the lamp type 3 is present.

The terms "level 1", "level 2" and "level 3" will be explained in more detail below in connection with FIG. 3.

If the difference resistance Rdiff falls within the stated limits and the lamp type can be determined by this, the setting of the operating parameters is continued according to the determined lamp type.

If, on the other hand, no range has been found in which the differential resistance Rdiff can be classified, then work continues with the last stored value.

Fig. 3 shows the course of the helical resistance in three different lamp types during the preheat phase, which lasts 500 ms.

For the first coil, the cold resistance Rcoldl X ₂ WW, and the hot resistance Rhotl y ₂ WW; where WW stands for a resistance value unit.

In the helix of the second lamp type, the cold resistance Rcold2 x ₃ WW. It rises during the preheat phase to the hot resistor Rhot2 with X ₅ WW.

The filament of the third lamp type starts with the cold resistance Rcold3 at x ₄ WW. This resistance increases during the preheat phase to the hot resistor Rhot3 with Xn WW. It can be seen how the resistance values spread with thermal heating. The prerequisite is that the coils during the preheating always the same heating power or the same heating current is supplied.

If the difference resistance is now formed in each case from the hot resistance Rhot and the cold resistance Rcold, a difference resistance Rdiffl of yiWW results for the first lamp type. The differential resistance Rdiff2 of the second lamp type is X ₅ WW. The differential resistance Rdiff3 for the third lamp type is Xi ₀ WW.

The spreading of the hot resistors Rhotl, Rhot2 and Rhot3 makes it possible to define for the differential resistors Rdiffl, Rdiff2 and Rdiff3 variation ranges which are spaced from each other. The variation ranges are marked with hatching lines.

A secure identification is in any case given if the determined difference resistance of the heating coil of a lamp falls into one of the three hatched areas.

However, it has been found that a satisfactory determination of the lamp type is possible even when working with the three drawn levels. The first level "level 1" is identical to the cold resistance Rcoldl of the first lamp type. The second level "level 2" is identical to the hot resistance Rhot2 of the second type of lamp. The third level "level 3" lies with a considerable distance above the hot resistance Rhot3 of the lamp type. With the distance arrows drawn on the right in the illustration, dashed lines show that the ranges of determination for the relevant lamp type extend beyond the lower undefined range to the next level.

The identification zones that go beyond the hatched areas are not compulsory, but have been chosen on a case-by-case basis. It is essential that the hatched areas, ie the variation ranges for the differential resistances, allow identification of the lamp type with great certainty.

Fig. 4a shows the dependence of the coil resistance R _w as a function of the filament voltage U _w . Two coils are considered, one having a helix resistance Ri and the other having a helix resistance R ₂ . The coil resistance R ₂ is twice as large as the coil resistance Ri. If the coil resistance Ri

R sets, so R ₂ = 2R. The coils are usually made of metal. The electrical resistance of

Metal increases with temperature. Without

Considering the thermal increase in resistance, the two helices form a parallel line to the abscissa, which is indicated by dashed lines. Taking into account the thermal resistance increase, the resistances of the two coils increase with increasing the filament voltage. The higher the heating power P supplied to a coil, the higher the corresponding thermal resistance increase. For the helix with the base resistance Ri, the heating power supplied is at an impressed helix tension Pi = U ² _W / R. For the coil with the base resistance R ₂ is the supplied heating power with impressed filament voltage P ₂ = U ² _W / 2R. The helix with the base resistance R ₂ supplied heating power P ₂ is therefore only half as large as the heating power Pi, which is supplied to the coil with the base resistor Ri. This has the consequence that the resistance of the coil with the base resistance R _{2 increases} with increasing coil voltage U _w less than the resistance of the coil with the base resistance Ri. The two curves approach each other with increasing coil voltage U _w . As a result, the distinction between two lamp types with the different coil resistances Ri and R ₂ becomes more difficult due to the thermal resistance increase.

4b now shows the idea underlying the invention, namely not to use an impressed filament voltage U _w , but instead an impressed filament current I _w . In this case, the heating power P ₂ = 2RI ² _W supplied to the coil with the base resistance R _{2 is} twice as high as the heating power supplied to the coil with the base resistance Ri, which is Pi = RI ² _W. It can be seen that the two curves diverge here, with the result that the thermal resistance increase improves the distinctness of lamp types after the coil resistance.

The dependencies of the filament resistance R "on the filament voltage U _w or on the filament current I _{w shown} in FIGS. 4 a and 4 b are illustrated in an idealized manner as straight lines. The influence of other parameters than the supplied heating power is disregarded for the sake of simplicity. If, in connection with FIG. 4a, an "impressed filament voltage U" is mentioned, it is meant that a predetermined filament voltage originating from a low-voltage voltage source is applied to the filament, and then the resulting filament current is measured. The helical resistance R _w then results from the product of filament voltage and filament current.

If, in connection with FIG. 4b, an "impressed helical current I _w " is mentioned, this means the following. Again, a helical tension is applied to the helix. However, this filament voltage is not specified, but only serves to set a predetermined specific filament current. The helical resistance R _w then results as a product of the preset and preset helical current and the helical voltage, which is necessary for this helical current to flow through the helix, and to be measured. Of course, an "impressed helical current I _w " can of course also be supplied by a high-impedance one, but the realization of this possibility causes practical difficulties, it is much simpler to adjust the helical current by regulation (changing the helical voltage) so as to set the desired one Takes value.

Fig. 5 shows a gas discharge lamp L, which is connected to a trained according to the invention electronic ballast V. The ballast V includes a connected to the AC mains bridge rectifier 1, which rectifies the mains voltage, and a DC voltage intermediate circuit 2 supplies. The intermediate circuit 2 is followed by a half-bridge inverter 3, the contains two alternately clocked switches. The inverter 3 is followed by a pure resonant circuit, which consists of a choke and a capacitor. The lamp is connected in parallel with the capacitor. The circuit parts 1 to 4 are common and known in ballasts.

The ballast should now be designed so that with him fluorescent lamps L of different types can be operated. The individual types differ not only by external dimensions, but also by different operating parameters, such as lamp current, lamp voltage, filament voltage, filament current, preheating, etc. It is common and well known that the ballast automatically detects the lamp type, by measuring the resistance at least one of the two coils of the fluorescent lamp L. However, the coil resistors of certain types are very close together, so that a distinction is difficult, and - as explained above in connection with Fig. 4a - is made even more difficult by the thermal heating. For this reason, in the case of the ballast considered here, the principle of the regulated helical current is used, which was described in connection with FIG. 4b.

Before the lamp type has been determined, the coils of the lamp L firstly a predetermined known Wendelstram must be supplied. This helical current is stored either in the block 5 representing operating parameter setting means or in a starting program (or programmer) 14 which transmits the relevant current value to the block 5 when it receives a corresponding command from a center via the bus Usus. The so transmitted current setpoint is supplied from the operating parameter setting means 5 a Wendelstromregier 8, which in turn causes Wendelspannungs-generating means 6, the two coils Wl and W2 of the fluorescent lamp L supply a corresponding filament voltage. The voltage applied to the lower coil W2 coil voltage is tapped with a voltage divider consisting of the resistors Rl and R2 and supplied to Wendelspannungsmessmitteln 9, which in turn pass the measured filament voltage value to a quotient-10. The filament current flowing through the filament W2 is measured as a voltage drop across a resistor R3 and supplied to Wendelstrom- measuring means 7, which in turn report the measured Wendelstromwert on the one hand to the quotient imager 10 and on the other hand as an actual value to the helical flow controller 8.

This forms a control value and transmits it to the helical voltage generating means 6, whereby the helical voltage is adjusted so that the helical current is equal to the setpoint supplied to the helical-current regulator 5. The quotient generator 10 calculates the filament resistance from the measured filament voltage value and the measured filament current value. The helix resistance is supplied to comparison means (decision logic) 13 which compares it with the values stored in a table stored in memory means 12. The table contains an associated coil resistance for each type of lamp to be operated with the ballast. This is compared with the measured coil resistance. The comparison means (decision logic) 13 then report the determined lamp type to the operating parameter setting means 5. Last then take the relevant settings on the ballast V before. vicarious for this is in Fig. 5 by the connection between the operating parameter setting means 5 and the inverter 3 taken into account. Thus, the clock frequency and / or the cycle times of the two switches of the inverter can be influenced in this way to set certain operating parameters.

It should be noted at this point that the quotient generator 10 is dispensable per se. Instead of storing in the storage means 12 a table which contains the correspondence between coil resistance and lamp type, it is also possible to set down a table containing the associated filament voltage for each lamp type - with known preset coil current. In this case, the filament voltage measuring means 9 would have to report the measured filament voltage instead of the heating resistor to the comparator means (decision logic) 13. The message of the filament current measured by the filament current measuring means 7, which takes place in FIG. 5 on the quotient formers 10, then disappears.

In Fig. 6, a concrete realization of the helical voltage generating means 6 is shown. These include a flyback converter, consisting of an electronic switch S, a resistor R4 and an inductance, wherein the inductance of the primary winding of a heating transformer T _{H is} formed. As a DC voltage source bus voltage U _Bu s lying on the bus is used. Instead of the _bus voltage U _bus , the output voltage of the intermediate circuit 2 can also be used. The heating transformer T _H has two secondary windings, each of which is intended for a filament of the fluorescent lamp L. The AC voltage transmitted by the heating transformer T _H is rectified by the diode 01 and 02 and by the Smoothed capacitors Cl and C2. In addition, the capacitors Cl and C2 still have the task to contribute to the radio interference suppression.

Claims

Method for determining operating parameters of a gas discharge lamp (L) to be operated with an electronic ballast (V), comprising the following steps:

a) preheating at least one heating coil (W1, W2),

b) measuring the filament voltage (U _w ) directly or indirectly

c) determining the value to be selected

Operating parameters by comparing measured values with stored reference values,

characterized in that

dl) during the measurement between the two times the helical flow or the helix power supplied to the helix is kept constant, or

d2) at the beginning of the preheating phase, a predetermined heating power or a predetermined heating current is set.

2. The method according to claim 1, characterized in that

e) the direct or indirect measuring of the filament voltage (U _w ) takes place at at least two different times, f) additionally the heating current is measured,

g) from the measurements of the filament voltage and the filament current at the first time of

Cold resistance (Rcold) and at the second time the hot resistance (Rhot) is calculated

h) from the hot resistance (Rhot) and the cold resistance (Rcold) the difference resistance (Rdiff) is calculated, and

i) is used as the measured value to be compared with the stored reference values of the difference resistance (Rdiff) determined according to point g) in order to determine an operating parameter.

3. The method according to claim 1 or 2, characterized in that step (dl) is realized by controlling the helical flow or the heating power.

4. The method according to any one of claims 1 to 3, characterized by the further step: i) setting at least one operating parameter for the determined lamp type.

5. The method according to any one of claims 1 to 4, characterized in that sets of reference values are stored, which apply to different preheating, such as filament current, filament voltage or heating power.

6. The method one of claims 1 to 4, characterized in that - if with the ballast (V) more lamps

(L1, L2) - a check is made to see if the lamps are of the same type.

7. The method according to claim 6, characterized in that for carrying out the test for Lampentypen- equality, the difference of the cold resistances (Rcold) formed by two lamps (Ll, L2) and compared with a first reference value (Rrefl), and that inequality is determined when the difference is greater than the first reference value.

8. The method according to any one of claims 1 to 7, characterized in that - if with the ballast (V) a plurality of lamps (Ll, L2) to be operated - a check is made thereupon whether a lamp is a fraction of a heating coil, whose voltage drop is measured to calculate the coil resistance (Rcold, Rhot).

9. The method according to claim 8, characterized in that for carrying out the test on Wendelbruch the difference of the cold resistances (Rcold) formed by two lamps (Ll, L2) and compared with a second reference value (Rref2), and that found a helical break when the difference is greater than the second reference value.

10. The method according to claim 9, characterized in that - if the measuring of the heating currents at several with the ballast (V) operated lamps (Ll,

L2) via a common resistor (R3) takes place - in the case of a diagnosed rupture of a heating coil (WIb, W2b), the values of the calculated coil resistances (Rcold, Rhot) corresponding to the fraction of the broken heating coil in the total number of heating coils whose heating current through the measuring resistor (R3 ) is reduced.

11. Circuit, in particular integrated circuit such as, for example, an ASIC, which is designed for carrying out a method according to one of the preceding claims.

12. Ballast (V) for at least one gas discharge lamp (L) with two heating coils (Wl, W2), comprising:

Means (8) for generating a constant filament current or a constant heating power and for charging at least one of the two heating filaments (W1, W2) with the constant heating current or the constant heating power,

- Measuring means (9) for direct or indirect measurement of the voltage drop across the helix (Wl, W2),

- means (7) for measuring the filament current,

- Storage means (15) for storing the measured values of the voltage drop across the helix (Wl, W2) and the helical current flowing through the helix, - means (10) for calculating the filament resistances (Rcold, Rhot) by quotient formation from the stored values for the measured filament current and the measured voltage drop across the filament (W1, W2),

Memory means (12) for a table in which a reference differential resistance value is stored for each lamp type for a given filament current or power, and - decision means (12) for determining the lamp type by comparing the calculated filament resistance (Rcold, Rhot) with the in reference coil resistance values set down to the storage means (12).

13. Ballast (V) for at least one gas discharge lamp (L) with two heating coils (Wl, W2), comprising:

Programmer means (14) defining two different times during the preheat phase at which the voltage drop across the filament (W1, W2) is measured, - means (7) for measuring the filament current,

- Storage means (15) for storing the measured values of the voltage drop across the helix (Wl, W2) and the helical current flowing through the helix to the two times predetermined by the programmer means (14),

- Means (10) for calculating the coil resistances (Rcold, Rhot) to the two of the programmer means (14) predetermined times by

Quotient formation from the stored values for the measured filament current and the measured voltage drop across the filament (W1, W2),

- storage means (12) for a table in which a reference differential resistance value is stored for each lamp type for a given filament current or heating power, and - decision means (12) for determining the lamp type by comparing the calculated differential resistance (Rdiff) with those in the storage means (12) reference differential resistance values.

14. Ballast according to claim 12 or 13, further characterized by

- means (5) for setting at least one operating parameter for the determined lamp type.

15. Ballast according to one of claims 12 to 14, characterized in that the means (8) for generating a constant filament current or a constant heating power comprise a regulator (8) for the filament current or the heating power.

16. Ballast according to one of claims 12 to 15, characterized in that the measuring means (9) for directly or indirectly measuring the voltage drop across the coil (W1, W2) acted upon by the predetermined constant filament current or the predetermined constant heating power comprise a voltage divider (R1, R2) connected in parallel with the heating coil include.

17. Ballast according to one of claims 12 to 16, characterized in that for measuring the filament current (8) with the heating coil (Wl, W2), a measuring resistor (R3) is connected in series, and that the voltage drop across this measuring resistor as a measured value for the helical current is used.

18. Ballast according to one of claims 12 to 17, characterized in that - when with the ballast two or more lamps (Ll, L2) are operated - by each a heating coil (WIb, WIb) of each of the lamps flowing helical current through the measuring resistor (R3) is guided.

19. Ballast according to one of claims 12 to 18, characterized in that when diagnosed fracture of a heating coil

(WIb, W2b) the value of the coil resistance (Rcold, Rhot) calculated by the means (10) corresponding to the fraction of the broken heating coil in the total number the heating coils whose heating current through the

Measuring resistor (R3) is reduced.