Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
1999-08-26
2002-06-18
Le, N. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S658000, C324S660000, C324S661000, C324S662000
Reexamination Certificate
active
06407557
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process for measuring the electrical resistance of a resistive body, possibly a resistive substance confined in a given volume, e.g. a conductive liquid contained in a reservoir, the resistance measurement being carried out without contact, i.e. in a non-destructive and non-intrusive manner. The invention also relates to a device for measuring the electrical resistance of a resistive body for carrying out the process and, by way of example, a device for measuring the quantity of a printing product contained in a reservoir, said printing product being resistive.
The invention also relates to a process for checking the conformity of a conductive liquid product contained in a reservoir. It also relates to a device for performing such a process. By way of example, the invention preferably relates to checking the conformity of a conductive printing product in a printer or other office machine incorporating such a printer.
As indicated above, the invention also relates in its operating principle to the measurement of the electrical resistance of a resistive body, because the information which is worked out by performing the process is directly related to the electrical resistance of an analysed resistive body. However, the invention can serve to measure and display any other magnitude, e.g. a quantity of product contained in a reservoir, if the variation in this magnitude is directly linked to that of the resistance by a known relationship.
DESCRIPTION OF THE PRIOR ART
The principle of a measurement of resistance without contact is already known in some applications. For example, U.S. Pat. No. 3,967,191 describes a process and a device for measurement of the electrical resistance of an internal film of a fluorescent lamp. The resistance of the film is measured by capacitive coupling. To achieve this, two metallic bands forming the plates of a capacitor are placed on the external wall of the lamp. One of the bands is connected to earth via a resistance, while the other is connected to a variable frequency generator via an inductance connected in series. Therefore, the whole constitutes a classic resonant RLC circuit, the resistance R being that of the internal film of the lamp. The frequency of the generator develops at relatively low frequencies, lower than or equal to 15 kHz. The inductance is selected and adjusted so that the resonance is produced during variation of the frequency in a given range. The amplitude of the resonance oscillations is measured to allow the resistance of the internal film of the lamp to be deduced.
Use of a variable frequency generator to detect the resonance frequency of an RLC circuit is a costly method and is a relatively slow process. In some systems, a measurement of this type must be made very rapidly and automatically without the knowledge of the user of the appliance, possibly to be able to prepare and display a message, i.e. to prevent operation of this appliance.
As for a printing machine one or more reservoirs of ink or pigmented product are to be found in an inkjet printer. In the following text the term “printing product” or even “ink” are used to refer to any liquid product which is appropriate for this use, including a colourless product known per se permitting better hold of the pigmented products on the paper. Only one reservoir is necessary if it is a black and white printer; if it is a colour printer, there are several reservoirs or compartments provided in the same cartridge which are filled with inks of different colours. Hence, in a high-quality colour printer, there may be up to seven cartridge reservoirs or compartments respectively enclosing inks of the following colours: black, dark cyan, light cyan, dark magenta, light magenta, dark yellow and light yellow. Therefore, it may be difficult for a person with little experience to easily replace or fill the reservoirs when necessary. While an error with black is rare, the risk of errors being made between two shades of the same colour is much more significant. Reversing light cyan and dark cyan reservoirs for example, can impair printing quality. The same applies for the other primary colours.
Moreover, the risks of errors differ according to the design of the printer. For example, in many printers an ejector head is closely associated with one reservoir. Sometimes, the print head is combined with the reservoir and is replaced at the same time as this, if it is a disposable reservoir.
If the system is based on one or more ink cartridges containing several reservoirs or compartments, as well as corresponding print head or heads, there is little risk of any handling error on the part of the user. However, this type of cartridge is expensive and its disposal may cause pollution. In fact, as soon as a reservoir or compartment is empty, the whole cartridge must be changed, which means that costly and polluting printing products are disposed of instead of being used. If the print head is separate from the reservoir or compartment which feeds it, an ink cartridge enclosing all the printing products allows errors to be avoided. Such a cartridge is more economical, but the pollution risks remain significant, since when a reservoir or compartment is empty, the whole cartridge must be changed.
Therefore, it may be preferred to use independent reservoirs, each reservoir possibly being associated with its own ink ejector head. In this case, an interchangeable reservoir only contains one single pigmented product. When one of these is empty, it is sufficient to replace only that one. However, the risks of error are much more significant.
There are also very significant risks of error when the printer comprises a number of reservoirs, which may be refilled by the user as and when required. In this case, there is the additional risk that a reservoir may be filled with an ink which is not appropriate, not only with respect to its exact colour, but also with respect to it quality, and use of such an ink may cause deterioration in the corresponding ink ejector head.
SUMMARY
In general, the process for measuring the electrical resistance in accordance with the invention is distinguished from the prior art in that it uses a resonant circuit comprising a variable capacitor forming means and in that the said resonant circuit is supplied with a fixed frequency. Advantageously, the variable capacitor forming means is a variable capacitance diode associated with an adjustable voltage generator, the advantage of this assembly being that it can be operated easily and quickly by varying the voltage applied to the diode, and the search for resonance and measurement of the corresponding peak amplitude can be operated in a very short time.
More precisely, the invention relates to a process for measuring the electrical resistance of a resistive body consisting of defining with said body a capacitance arrangement formed from a capacitive branch comprising at least one capacitor electrically connected to said resistive body and incorporating this capacitive section in a resonant circuit, characterised in that this resonant circuit additionally comprises a variable capacitor forming means, said resonant circuit being supplied with a fixed frequency, the capacitance of said capacitor being varied by measuring a signal delivered by said resonant circuit, the peak amplitude of this signal being measured and the value of this peak being representative of the resistance of said body.
As indicated above, the variable capacitor forming means preferably comprises a variable capacitance diode and an adjustable voltage generator connected to apply an inverse voltage to the terminals of said diode. The implementation of the process therefore consists simply of varying the capacitance of the capacitor by varying the voltage of the voltage generator according to a predetermined law. During this time, a peak amplitude detector connected to the resonant circuit allows said peak to be identified and its amplitude measured.
If the magnitude which has to be measured and checked is not, s
Coudray Pascal
Froger Marie-Helene
Lorgeoux Mickaël
Truffaut Christophe
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Hamdan Wasseem H.
Le N.
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