Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Frequency of cyclic current or voltage
Patent
1981-04-03
1988-10-11
Eisenzopf, Reinhard J.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Frequency of cyclic current or voltage
318611, 318621, 318632, G01D 302
Patent
active
047774282
DESCRIPTION:
BRIEF SUMMARY
The present invention consists of a device for compensation of electrical transfer functions of electric or electronic sensors, instruments or fourpoles.
When mesuring for instance temperatures by the use of thermo element or thermistor instruments or when measuring optical radiation by the use of thermopile radiometers or some pyroelectric radiometers, the rise time of the instrument in many cases is very long compared to the duration of the variations of the signal being measured, and often constitutes a problem.
The rise time of thermopile detector is often in the order of a half to one minute. When for instance a radiation with fast variations (within seconds or parts of) is measured, the signal available on the output terminal of the instrument, as a rule does not have the slightest similarity with the unit being measured. This is due to fact that the modulation transfer function (MTF) of the detector is not linear within the actual frequency range. In these cases the instrument or detector is often said not to be fast enough. Then it is of no consquence that the amplifier to which the detector or instrument is connected is fast and has a linear transfer function.
There are a large amount of instruments and devices where the detector or sensor is sensitive but too slow for measuring fast processes. In these cases a device in accordance with the present invention would make the instrument suitable also for measuring signals with rapid variations. Instruments, which are sensitive but slow are made by the most advanced instrument manufacturers in the worlds leading industrial nations and well known.
As it undoubtedly is of great value to have instruments with shorter time constants, so far simple methods of realizing this with instruments having slow sensors have been unknown. On the other hand, the increasing of the time constant of a fast instrument has never been a problem.
SUMMARY OF THE INVENTION
The present invention solves these problems in the way that is described in the distinguishing part of the attached (main)claim. It is anticipated, that the sensor, detector or four pole, of which the transfer function is to be compensated, is connected to the non-inverting input of a high amplification differential amplifier the output of which is connected to an output terminal as well as, through a feed-back network, with a transfer function arranged to be as similar with the transfer function of the sensor, detector or four pole as possible, to the inverting input of the differential amplifier.
It may be suitable to let the feed-back network consist of a number of adjustable filters. Alternatively as a rule it is possible to use passive filters. The filter types referred to in these cases are proportional filters, deriving and integrating filters.
It may also be suitable to bypass the compensating device, constituted by the present invention, without having to disconnect it electrically.
It is suitable to have a switch, that connects the signal from the sensor, detector or four pole directly to the output terminal of the device while the differential amplifier with its feed-back network is arranged to be disconnected.
Finally it might be suitable to make the compensating device, constituted by the present invention, as a separate unit, that can be connected between the instrument of which the tranfer function is to be compensated, and a read out unit such as a dial instrument or a writing oscillograph.
DESCRIPTION OF THE FIGURES
An example of how the compensating device can be made in accordance with the present invention, is described in detail with reference to the attached FIGS. 1-5, thus
FIG. 1 shows the output from a typical sensor when the measured unit is a step function,
FIG. 2 shows a sensor,
FIG. 3 shows a four-pole,
FIG. 4 shows the fundamental arrangement of a compensating device in accordance with the present invention and
FIG. 5 shows a more complete compensating device in accordance with the invention, made as an external accessory for an instrument.
DESCRIPTION OF A PREFERRED EMB
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Eisenzopf Reinhard J.
Solis Jose M.
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