Optical transmitter for producing an optical signal indicative o

Details Optical transmitter for producing an optical signal indicative o Optical transmitter for producing an optical signal indicative o

1991-06-24

1994-12-20

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

374176, G01D 534

Patent

active

053748220

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to an optical transmitter for producing an optical signal indicative of the temperature of a component, such as a spark plug, operating under high tension. Such an optical transmitter is known (DE-C-2512634). The thermoelectric voltage from a hot junction on the tip of the insulator of the spark plug is applied to a voltage controlled oscillator (VCO) whose output frequency is thus dependent on and preferably proportional to the temperature to be measured. The oscillator output is fed to a light-emitting diode (LED) and the resulting pulsed optical signal is transmitted along an optical conductor to a light sensitive semi-conductor component where it is re-converted to an electrical signal. The electrical signal can be processed for further use, such as for the digital or analog display of the temperature or for appropriate control of the operation of the internal combustion engine to which the spark plug is fitted. The optical conductor electrically isolates the optical transmitter and thereby the thermoelectric element and its lead wires from the processing circuitry. Thereby the risk of arcing between the centre electrode of the spark plug and the thermo-electric element and its lead wires is minimized. By arranging the optical transmitter as close to the spark plug as possible, the radiation of interference and the capacitive loading on the ignition system are minimized. However, the sparks produced at the spark plug themselves have a very high frequency component (<10.sup.9 Hz) and this can interfere with the evaluation of the measured voltage.


SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide an optical transmitter which avoids the disadvantages of the prior art.
In keeping with these objects and with others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in an optical transmitter for producing an optical signal indicative of the temperature of a component, such as a spark plug, operating under high tension, wherein a voltage dependent on the temperature to be measured, such as a thermoelectric voltage from a thermocouple hot junction in the component whose temperature is to be measured, is converted into an optical signal which is transmitted along an optical conductor to a light sensor, wherein in accordance with the invention the lead wires which transmit the temperature-dependent voltage are connected to an optical transmitter via a low pass filter which is contained within a housing of ferromagnetic material and the housing is held at the high tension at which the component, whose temperature is to be measured, stands, and is itself surrounded by insulating material.
The low pass input filter prevents the high frequency interference from reaching the VCO or other circuity of the optical transmitter and the ferromagnetic housing screens any interference radiation from the filter itself. Interference suppression is thus very effective.
Filtering of the high frequency interference is further improved by constructing the low pass filter electrically and mechanically symmetrical. In particular, the low pass filter is electrically symmetrical with respect to the ferromagnetic housing. The low pass filter can comprise at least one capacitor between the lead wires and at least one respective capacitor between each lead wire and the ferromagnetic housing. It can include a respective inductance in each of the lead wires. Filtering is also improved by the use of lead-through capacitors between the filter and the VCO.
To avoid radiation of interference from the ferromagnetic housing, an outer casing can be provided. The outer casing can be formed as a metallic outer casing coupled at earth potential. The metallic outer casing at least where it surrounds the insulating material on the ferromagnetic housing of the low pass filter can be constructed symmetrically.
Faulty readings can be further avoided by arranging the components of the optical transmitt

REFERENCES:
patent: 4697920 (1987-10-01), Palm et al.
patent: 5270538 (1994-01-01), Wlodarczyk et al.

Affiliated with

Also associated with

Rating

Optical transmitter for producing an optical signal indicative o does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Optical transmitter for producing an optical signal indicative o, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical transmitter for producing an optical signal indicative o will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2387526