Patent Application
20080217518
The present invention relates to an electronic detecting apparatus and particularly but not exclusively relates to an electronic detecting apparatus for detecting the output of an external device such as a light emitting device for example.
It has previously been proposed, for example, to provide an electronic light power detecting apparatus comprising a detector that produces an output voltage or current which is proportional to the difference in temperature between one side of the detector and the other, one of the sides of the detector being impinged, in use, by light energy from the light source whose power is being measured. Such a detector may use the Peltier-Seebeck effect.
The output voltage typically rises in a relative slow fashion as the exposed side of the detector heats up, until a steady state is reached wherein the detector is in thermal equilibrium. A constant or varying temperature difference may exist across the detector.
The time taken for the detector to reach the steady state wherein the output voltage is indicative of the power of the light emitting device being detected is often therefore relatively long.
According to one aspect of the invention there is provided an electronic detecting apparatus for detecting an output of an external device, the apparatus comprising a detector operative to detect a variable relating to the output of the external device, and a controller operative to receive a detector signal from the detector indicative of an initial non-steady state value of the detected variable and further operative to process the detector signal to generate a processed signal, the controller combining the detector signal and the processed signal to generate an output signal indicative of a future steady state value of the variable.
Thus, when there is a change in the level of the output of the external device being detected, the output signal of the detecting apparatus is generated more quickly than the detector signal itself.
Preferably the controller is subsequently operative to process the output signal to generate a display control signal to a controller display to indicate the output of the external device.
Preferably the display comprises part of the electronic measuring apparatus.
Preferably the controller comprises a differentiator operative to generate the processed signal, the processed signal being proportional to the rate of change of the variable of the external device detected by the detector of the detecting apparatus.
The controller may comprise electronic circuitry.
The differentiator may comprise a differentiator sub-circuit comprising a resistor and a first operational amplifier connected in parallel, an input to the first operational amplifier being an output from the detector.
Preferably a gain adjuster is provided to enable the apparatus to be adjusted in order to be able to detect a range of amplitudes of variable of the external device.
Preferably a combiner is provided to combine the detector output and the processed output from the differentiator.
The combiner may comprise a response speed adjuster operative to adjust the response speed of the combiner in order to achieve a desired balance between speed and accuracy of response.
The combiner may comprise electronic circuitry comprising a second operational amplifier, a first input to the second operational amplifier being the output from the detector, a second input to the second operational amplifier being the output from the differentiator sub-circuit.
Preferably a signal compensator is provided operative to generate a compensation signal to adjust the output signal to compensate for errors in the detector output.
Preferably the signal compensator comprises a signal compensation sub-circuit comprising a capacitor and a resistor connected in series with the first input of the first operational amplifier.
Preferably the electronic circuitry comprises a preamplifier operative to amplify the output of the detector.
The apparatus may comprise a light power detecting apparatus. The apparatus may comprise a laser power detecting apparatus.
The detector may comprise a Peltier-Seebeck detector, that is, a detector that produces, in use, an output voltage proportional to heat transfer across the detector.
According to another aspect of the invention there is provided a light power detecting apparatus for detecting the power of a light emitting device, the apparatus comprising a Peltier-Seebeck detector operative to detect light emitted from the light emitting device, and control means operative to receive a detector signal from the Peltier-Seebeck detector indicative of an initial non-steady state value of the emitted light and further operative to process the detector signal to generate a processed signal, the control means combining the detector signal and the processed signal to generate an output signal indicative of a future steady state value of the power of the light emitting device.
According to a further aspect of the invention there is provided an electronic detecting apparatus for detecting an output of an external device, the apparatus comprising a detector operative to detect a variable relating to the output of the external device, and control means operative to receive a detector signal from the detector indicative of an initial non-steady state value of the detected variable and further operative to process the detector signal to generate a processed signal, the control means combining the detector signal and the processed signal to generate an output signal indicative of a future steady state value of the variable.
Other aspects of the present invention may include any combination of the features or limitations referred to herein.
The present invention may be carried into practice in various ways, but embodiments will now be described by way of example only with reference to the accompanying drawings in which:
a to 2d are graphs of voltage against time for various components of the circuitry of
a to 3e are graphs of voltage against time for various further components of the circuitry of
a to 4c are further graphs of voltage against time for various components of the circuitry of
An electronic detecting apparatus, which in this example comprises a light power detecting apparatus, comprises a light detector, an output signal display, and a power source to power the detector and the display. Electronic control means comprising a controller is provided to receive and process a signal from the detector in order to generate an output signal to indicate on the display the power of an external light emitting device such as a laser for example.
Referring to
The detector voltage output 3 is amplified by a preamplifier 5 before being input, via a parallel circuit connection, to compensation means comprising a compensation sub-circuit 7, and to combining means comprising an addition/subtraction sub-circuit 9.
The compensation sub-circuit 7 comprises a series capacitor 11 and resistor 13 that are connected in parallel with a second capacitor 15.
A voltage output 17 from the compensation sub-circuit 7 passes, via a further resistor 19, to differentiating means comprising a differentiator sub-circuit 21 comprising a first operational amplifier 23 and a resistor 25.
The first operational amplifier 23 comprises a first, non-inverting input 27 connected to earth 4, and a second, inverting input 29 connected in series to the compensation sub-circuit 7. The first operational amplifier 23 generates a processed output comprising a differential output voltage 33 that is an amplification of the difference between the voltage from the power source 4 and the voltage output 17 from the compensation sub-circuit 7.
The differential output voltage 33 is fed, via a resistor 35, to the addition/subtraction sub-circuit 9 and in particular to the inverted input 39 of a second operational amplifier 41. The non-inverted input 43 of the second operational amplifier 41 receives the amplified detector voltage output 3 from the preamplifier 5.
The addition/subtraction sub-circuit 9 is operative to combine the detector output 3 and the processed output 33 by subtracting the inverted differential voltage output 33 of the differentiator sub-circuit 21 from the original, non-inverted pre-amplified detector voltage output 3 to provide an output voltage signal 44 indicative of the predicted future steady state power of the light emitting device. The output voltage signal 44 is converted into a display output indicative of the power of the light emitting device being measured, for displaying on a display (not shown), such as an LCD or LED display, that may be integral with, or separate to, the electronic detecting apparatus.
The gain of the differentiator sub-circuit 21 can be adjusted using a variable resistor 45 to give an output voltage signal 44 indicative of the absolute instantaneous power of the light emitting device.
Referring additionally to
An instantaneous change in input power as per the step input of graph 2a) causes the detector output voltage 3 (or amplified detector output voltage) to rise from an initial value V0 to a final value V1.
If the response of the detector 1 conforms to a single pole exponential response with time constant k the detector output voltage 3 (V) at time t after the input step is given by:
V=V
0+(V1−V0)(1−e−t/k)
or V=V1−(V1−V0)e−t/k
The rate of change of the output voltage V over time, dV/dt, is given by:
dV/dt=(1/k)(V1−V0)e−t/k
If this is multiplied by a factor a (with dimensions of time) and added to the original output V, a summed output Vs is produced:
Putting a=k gives Vs=V1, i.e. the summed output voltage value goes immediately to its final value to produce the output voltage signal 44.
As can be seen from a comparison of graphs b) and d), in use, the apparatus predicts the final steady state power of the light emitting device many times more quickly than the time that would be taken for the apparatus to reach steady state using only the detector voltage output 3 and thus more promptly provides an accurate indication to the user of the apparatus of the power of the light emitting device.
The above description assumes that the response of a Peltier-Seebeck detector to radiant light energy provides a simple, single pole exponential response. However, typically a Peltier-Seebeck detector does not exactly provide such a response. Referring to
This problematic response is overcome by the compensation sub-circuit 7 comprising the series capacitor 11 and resistor 13. The compensation voltage output 17 from the compensation sub-circuit 7 can be seen with reference to graph 3d). The output voltage signal 44 of the apparatus is then a combination of the output 33 of the differentiator sub-circuit 21, which itself receives the output 17 from the compensation sub-circuit 7, and the amplified detector output voltage 3 of the detector 1 itself. This final output signal 44 can be seen with reference to graph 3e) and closely replicates the step input from the light emitting device, with the final steady state power of the light emitting device being determined in a relatively short time.
Graph 4a illustrates a pulsed output from an external device, with Graph 4b illustrating the normal, ie non speeded up detector output voltage 3. Graph 4c illustrates the final output signal 44 of the device 1.
The differentiating means and the integration means could comprise any suitable componentry including, for example, analogue electronic components such as operational amplifiers and/or electronic processing means such as for example micro processors.
Whilst the above described embodiment relates to a light power detecting apparatus comprising a Peltier-Seebeck detector, the apparatus could comprise any other type of detecting apparatus using any desired type of detector.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0704548.7 | Mar 2007 | GB | national |
