GB2166544A - Device for phase synchronisation for step drive controlled modulation devices - Google Patents

Abstract

A phase synchronisation device for a step-drive controlled modulation device, particularly for use in spectral photometers, comprising a detector which is non-displaceably arranged relative to the modulation device for producing a synchronisation signal. The latter synchronizes a counting operation of a pulse sequence directly derived from the clock-pulse of the control frequency of the step-drive for the modulation device. The counting operation is reduced in the pulse length. The pulse sequence is time delayed and adjustable. Evaluation signals are obtained from the counting operation in a logic member, which signals are used for the evaluation stages of the electrical signals corresponding to the optical signal of the spectral photometer. <IMAGE>

Description

SPECIFICATION Device for phase synchronisation for step drive controlled modulation devices The invention relates to a device for phase synchronization for step drive controlled modulation devices, particularly for use in multibeam spectral analysis devices.

The invention can be utilized in all those cases where optical paths of beams are mechanically or optically modulated and electrical evaluation signals have to be derived in phase in order to process electrical measuring signals which have been produced by means of the optical device. Further particular fields of application are photometers, calorimeter and other physico-optical analysis measuring devices.

DD-PS 65168 dicloses an analysis measuring device in which the drive of an optical modulation device is performed by a synchron motor. Modulation devices based on rotating reflectors and/or diaphragms, produce, when used in double beam photometers, at least two signals to be evaluated, namely a measuring signal and a reference signal. With devices which include microprocessors for evaluation and control it is advantageous for increasing the measuring precision also to measure the zero signal within one modulation period.

After amplification in an a.c. amplifier the average value of the measuring, reference and zero signals which appear in time sequence is lost. This average value is regained by a socalled clamping circuit. Further evaluation signals for the electrical evaluation of the optical signals are required for the integrator release, the integrator clearing, the A/D converter start and the indentification of the measuring signals, the reference signals and the zero signals.

Such evaluation signals, as generally known, are derived by a plurality of detectors (for example, opto-couplers) from the modulation device, which includes control discs or control tracks. To this end, the detectors have to be very accurately mechanically adjusted and have to be provided with respective position-variable mounting and displacement means which require comparatively high technological and economical expenditures.

Since the adjustment has to be performed with the device in operation, neither the optical path of beams has to be interrupted nor stray light is permitted to enter the path of beams during adjustment. Under these conditions, an exact adjustment involves high time expenditures and a complicated technical handling operation.

In addition to the aforegoing, the numerous mechanical adjustment members reduce the reliability of the phase synchronisation.

Furthermore, it is known from DE-OS 3 202 807 to use a step-motor for a light chopper in a spectral analysis device.

The light beam chopper, driven by a servomotor, produces a pulsating light beam. A device responsive to this light beam is used to produce a phase synchronous demodulating signal. A high frequency clock-pulse signal is stepped down by a divider circuit before being applied to the step-motor.

In order to generate a demodulation signal, one starts via frequency dividers from the same high frequency clock-pulse signal which is divided by a divider arrangement until the same frequency as the light beam frequency is obtained. Starting from the optical signal of the analysis device, the demodulation signal is phase-synchronized with the scanning signal (=optical measuring signal) by a detector and a zero point detector connected thereto. The detector is, simultaneously, used to generate the scanning signal, that is, the signal after passage through the optically active sample, and to generate the demodulation signal. This demodulation deteriorates and fails entirely, respectively, at higher absorptions of the optical sample owing to noise. The disclosed solution is only suitable for single beam devices.

It is an object of the present invention to reduce the technical and economic expenditures and those for the adjustment, as well as to increase the reliability.

It is a further object of the present invention to provide a rather simple and quickly adjustable device for phase synchronisation for stepdrive controlled modulation devices, particularly for multi-beam spectral analysis devices, without involving any mechanical adjustment members.

According to the present invention there is provided a phase synchronization device for step-drive controlled modulation devices, particularly for use in multi-beam spectral analysis devices. The invention comprises a modulation device which is step-drive controlled and includes reflectors and/or diaphragms which, in turn, trigger and switch-over a measuring light beam from a measuring channel to a reference channel. It further includes a counter controlled by the step-drive clock-pulse, and a means for generating evaluation signals for "clamping/clear", for "A/D conversion" and for "identification of the optical signals", which are applied to evaluation stages for the analog and digital processing of the electrical measuring signals derived from the optical signals.

The input for the control frequency of the step drive is connected to the count input of a counter via a delay stage, which is preferably a monostable multivibrator and time variable, and via a following pulse cutting stage.

A non-displaceable detector is arranged adjacent the modulation device, preferably embodied as an opto-electronic reflex-coupler, with a subsequent threshold value stage which produces a synchronization signal phase coupled to the optical signal and which is independent of the signal information of the latter, for resetting the counter via a pulse reduction stage. A logic correlation stage is connected to the count outputs and carry-on outputs of the counter for producing the evaluation signals.

Advantageously, the logic correlation stage comprises bistable flip-flop stages set, reset and triggered by the count and carry-on outputs of the counter for generating the evaluation signals for the "clamping/clearing" and the "A/D-conversion" and a counter for generating the evaluation signal for "identification of the optical signals" at the count input of which an evaluation signal is applied formed by the bistable flip-flop stages, and at the reset input of which the pulse reduced synchronization signal is applied.

A synchronization signal is produced from a non-displaceable detector arranged at the modulation device independent of the signal information of the optical analysis signal.-By means of this synchronization signal, which is even produced when the optical analysis sample is highly absorbing unaffected by the latter, the entire evaluation signals are produced exclusively electrically for control of the evaluation stages, as well as for the signal identification (particularly in multi-beam analysis devices) which hitherto have been adjusted by cumbersome mechanical settings, by logical correlation of an adjustably delayed and pulse length reduced pulse sequence which is online derived from the control frequency for the step-drive of the modulation device.

On by one detector arranged at the modulation device, which detector does not serve as an adjustment member for phase synchronisation, are the entire evaluation signals derived via logical correlations for control of the evaluation stages for the evaluation of the electrical measuring signals equivalent to the optical analysis signal. The adjustment of the entire synchronisation process in the course of producing the evaluation signals mentioned is feasible at a low expenditure and with a high reliability by the electrical adjustment of only one adjustment element (the controller of the time delay stage embodied by the one-shot hot multivibrator).

The logical operation for formation of the individual evaluation signals can be technically realised by numerous possibilities.

It has proved very advantageous, particularly for reasons of application, to set, reset and trigger with the count and carry-on outputs of the counter synchronized by the pulse length reduced synchronization signal, the flip-flop stages at the outputs of which at first the evaluation signals for "clamping/clearing'' and then for "A/D-conversion" are provided. One of these evaluation signals actuates a further counter which is reset by the pulse length reduced synchronisation signal. At the output of this counter the evaluation signals for "identification of the optical signals" are provided.

The arrangement according to the invention is not restricted to any particular construction of the modulation device since the latter has not to include special components such as additional control discs or control tracks for the phase synchronisation.

The detector, for example, the opto-coupler which has to be non-displaceably attached to the modulation device is directly aligned to the reflector and aperture, respectively, anyway present for modulation.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic view of a device according to the invention for producing and adjusting evaluation signals.

Figure 2 is a schematic view of evaluation stages for processing the electrical measuring signals equivalent to the optical analysis signals; and Figure 3 shows pulse diagrams for phase synchronisation.

The overall arrangement of a double-beam spectrometer operable in the UV-vis-range which incorporates a device according to the invention comprises a light source emitting a radiation beam which passes a monochromator for producing monochromatic light, a bipartite rotating reflector and a rotating light stop.

The monochromatic radiation is switched over and interrupted by this reflector/light stop combination. The split monochromatic radiation propagates along a reference path and along a sample path, that is, a sample to be analysed is inserted into the sample path, hereinafter referred to as measuring path. The optical analog signals produced in this manner contain, separated in time, the analog reference signal R, the measuring signal M and the zero signal N in each modulation period.

These signals impinge upon a photo-multiplier 17 (Fig. 2) the operation of which is expiained in more detail in connection with Fig. 2.

The position of the modulation reflector and of the light stop relative to a selectively excited, but resting, step-motor is adjusted when the entire unit is assembled, as well as the position of a reflex coupler (sensor) relative to the path of the monochromatic radiation. The step motor employed for rotating the bipartite reflector has an angular step width of 6". For one modulation period of 180", 180" =30 steps are required.

6" Due to the computer-controlled high speed run of the step-motor after switching on the device, the hitherto required starting clutch can be dispensed with when driven by a synchronous motor. The modulation frequency of 40 Hz is produced with a clock-pulse frequency of 1.2 cps.

In Fig. 1, the device according to the invention for producing and adjusting the evaluation signals for phase synchronisation is shown.

Only the step-motor 2 and the rotating bipartite reflector 3 are known from the general description of the spectrometer; the light stop mounted on the same axle is omitted. A clock-pulse frequency Ts of a frequency of 1.2 cps controls a step drive unit including the member 1 and the step-motor 2 which rotates the modulation reflector 3. The modulation device serves to optically trigger and switch-over the (not shown) monochromatic radiation from the measuring path to the reference channel and to produce the zero signal. An opto-electronic reflex-coupler 4 is non-displaceably arranged adjacent the modulation reflector 3.

The radiation 4' emitted by the reflex-coupler 4 is reflected at the reflector 3, when in a respective rotational position, and returns as a radiation 4" to the reflex coupler 4. In this manner the latter is switched by the movement of the modulation reflector 3. The voltage supply of the reflex coupler 4 is indicated by two resistors 41 and 42. The reflex coupler 4 produces via a threshold 5 and an inverter 6 a synchronisation signal S, the timely course of which relative to the optical signal (the monochromatic radiation) of the analysis device (Fig. 3a) is shown in Fig. 3b. The optical signal, the synchronisation signal S and the clock-pulse frequency T,. (Fig. 3c) have a defined phase relation.A pulse length reducing stage 7 produces from the LH-edge of the synchronisation signal S a signal 8 for clearing (reset) of a counter 13 which is a decimal counter in the present example. The clockpulse frequency T, further triggers a one-shot multivibrator 11 which by its holding time tH produces the pulses according to Fig. 3d, the holding time tH being defined by a resistor 9 and a capacitor 10. The resistor 9 is variable so that the holding time tK is electrically adjustable.The multivibrator 11 controls, via a pulse length reduction stage 12, the count input of the counter 13 through counting pulses Tz (Fig. ?.e). The count and carry-on outputs QA, Qo, U of the counter 13 are connected to a logic member formed by two D-flip-flops 14, 15 and a two bit counter 16. The D-flipflop 14 produces the evaluation signal "Clamping/Clear" (Fig. 3 1) which is obtained as follows: the carry-on signal Uv (Fig. 3h) from the counter 13 sets the D-flip-flop 14, and the subsequent LH edges of the output signal QA of the counter 13 (Fig. 3f) triggers the D-flipflop 14. The evaluation signal "Clamp/Clear" returns to L potential since L-potential is applied across the D-input of the D-flip-flop 14.

The D-flip-flop 15 supplies the evaluation signal for "Analog/Digital conversion" ("AD start"). It results from the LH edge of the QA output signal of the counter 13 at D=H, that is, from the transition from the counter state "8" to the counter state "9" of the counter 13. The carry-on signal Üv (Fig. 3h) of the counter 13 resets the output signal of the Dflip-flop 15 via the R-input to L-potential. This output signal (evaluation signal "analog-to-digital conversion") controls at the same time the count input of the two bit counter 16 which is reset by the pulse length reduced synchronisation signal S. The first subsequent output signal from the D-flip-flop 15 switches the counter state of the two-bit counter 16 to "1".

This counter state characterises the reference signal (Fig. 3a) of the analog signal. The subsequent output signals of the D-flip-flop 15 switch the counter states of the two-bit counter 16 to "2" and "3". The counter state "2" designates the measuring value and the counter state "3" the zero-value of the analog signal (Fig. 3a).

In this manner the evaluation signals for "identification of the optical signal" are derived from a logic combination of the evaluation signals "analog-to-digital conversion" ("A/D-start") and the pulse length reduced synchronisation signal S.

Fig. 2 shows in a very simplified form the analog amplifier for the electrical processing of the optical signals emitted by the light source modulated by the modulation device and passing the reference path and the measuring path, respectively, and subsequently impinging upon the photomultiplier 17. The photomultiplier 17 converts the impinging monochromatic radiation and feeds the analog electric signals into an amplifier 18. A capacitor 19 separates the d.c. portion from the analog electric signals. A switch 20 connects the potential at the input of an amplifier 21 to a zero-voltage provided that the photomultiplier 1 7 is blanked out by the (not shown) light stop. The switch 20 is controlled by the evaluation signal "Clamping/Clear".An integrator, formed by a resistor 22, an amplifier 23 and a capacitor 24, subsequently integrates the signals R, M, N of the analog electric signal (Fig. 3k). The integrator is cleared between the signals R, M, N by a switch 25. This is obtained again, as indicated, by the evaluation signal for "Clamp/Clear". An A/D converter 26 is started by the evaluation signal for "analog-todigital conversion" (A/D-start) (Fig. 3g) and subsequently digitizes the analog integrated signals R, M, N. The A/D-start at "High" po potential of the synchronization signal S characterizes, for example, the digitized value of the signal R. This is followed with the next evaluation signals at "A/D-start" by the digitized values of the signals M and N of the analog signal.The A/D converter can be replaced, with a slight modification of the circuitry, by a voltage frequency converter. This is ON for the period of the signals R, M and N.

Figs. 1 and 3 show that the expenditures for the control signals (Fig. 1) are very low at an appropriate selection of the signal lengths R, M, and N, expressed in degree of angle, and of the step angle of the step-motor.

In Fig. 3 the already mentioned signal curves as a function of time are shown in diagrams in order to better exemplify the operation of the circuits.

Fig. 3 the signals are plotted versus time, related to the angle of rotation of the reflector/light stop combination.

180 correspond to a duration of period of 1 1 T== =25 ms.

f 40 Hz Fig. 3a curve of the analog signal as produced by the reflector/light stop combination in the photometer. It contains, in time sequence, the signals: reference R, measuring M, zero N.

For reasons of simplicity the phase shift of the electronic amplifier is zeroed. Hence, Fig.

3a represents the optical as well as the electrical analog signal.

Fig. 3b synchronisation signal S as produced from the reflex-coupler 4 by means of the modulation reflector 3 which switches the optical path of beams. The LH-edge is utilized for clearing the counter 13, and the H-signal for identification of the reference signal R.

Fig. 3c: clock-pulse frequency T from the micro-computer for the step drive.

Fig. 3d: output signal Q of the mono-stable multivibrator 11. The LH-edge is derived from T < . Hold-time TH is adjustable via the resistor 9.

Fig. 3e: clock-pulse signal T, for the counter 13, derived from the HL-edge of Q of the mono-stable multivibrator 11.

Fig. 3f, g: Output signals QA and QD of the counter 13.

Fig. 3h: forward carry ij, of the counter 13.

Fig. 3i: clamping and clear signal K/L for the analog amplifier according to Fig. 2, derived from U, and the LH-edge from QA of the counter 13.

Fig. 3j: A/D-start A/D st for the A/D-converter in Fig. 2 produced from the LH-edge of QA at QD=H and U, of the counter 13.

Fig. 3k: signal at the integrator output and input of the A/D-converter, respectively.

At the respective point of time of the LHedges of A/D st the integrated values of R, M, and N are provided which are digitized.

Claims (5)

1. A phase synchronisation device for step-drive controlled modulation devices, such as multi-beam spectral analysis devices comprising a modulation device which is to be step-drive controlled, reflectors and light stops for optically triggering and switch-over of a light beam from a measuring channel to a reference channel, and vice versa, said light beam being provided for measuring value evaluation, a counter controlled by a stepdrive clock-pulse, and means for generating evaluation signals for "clamping/clear, for "A/D conversion" and for "identification of the optical signals", which are applied to evaluation stages for the analog and digital processing of the electrical measuring signals derived from the optical signals, the input for the control frequency of the step drive being connected to the count input of a counter via a delay stage and via a following pulse length reduction stage, a non-displaceable detector being arranged adjacent the modulation device with a subsequent threshold value stage for producing a synchronization signal phase which is coupled to the optical signal and is independent of the signal information of the latter, for resetting the counter via a pulse length reduction stage, and a logic correlation stage being connected to the count outputs and carry-on outputs of the counter for producing the evaluation signals.

2. A phase synchronisation device as claimed in claim 1, wherein said delay stage is a mono-stable multivibrator which is time-adjustable.

3. A phase synchronisation device as claimed in claim 2, wherein said detector is an opto-electronic reflex-coupler.

4. A phase synchronisation device as claimed in claim 3, wherein the logic correlation stage comprises flip-flop stages set, reset and triggered by the count and carry-on outputs of the counter for generating the evaluation signals for the "clamping/clearing" and the "A/D-conversion, and a counter for generating the evaluation signal for "identification of the optical signals", at the count input of which an evaluation signal is applied formed by the flip-flop stages, and at the reset input of which the pulse length reduced synchronisation signal is applied.

5. A phase synchronisation device for step-drive controlled modulation devices, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.