Photoelectric control unit adapted for determining its own operating margin having dual variable-gain amplifier

• US 5,281,810 A
• Filed: 12/30/1992
• Issued: 01/25/1994
• Est. Priority Date: 12/30/1992
• Status: Expired due to Term

• Current Assignee: Allen-Bradley Company (Rockwell Automation, Inc.)
• Original Assignee: Allen-Bradley Company (Rockwell Automation, Inc.)
• Inventors: Johnson, Philip E., Delaney, Patrick J. III, Fooks, Elik I.
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): LE, QUE TAN
• Application Number:
  US07/998,976
• Time in Patent Office: 391 Days
• Field of Search: 250/222.1, 250/221, 250/214 A, 250/214 AG, 340/555, 340/556, 340/557, 307/311
• US Class Current: 250/222.1
• CPC Class Codes: G01V 8/10 Detecting, e.g. by using light barriers by reflection from the object G01S17/00
• CPC Class Codes: H03K 17/941 using an optical detector H03K17/968 takes precedence
• CPC Class Codes: H03K 5/086 generated by feedback

Abstract

A photoelectric control unit including an electronic system having a system architecture which is adapted for allowing the unit to readily and accurately determine its own operating margin. This architecture system includes a pair of variable gain modules which operate in conjunction with a pair of separate signal channels. The signal channels have comparators for comparing signal amplitudes on their respective channels with a common reference level. Operating margin values are determined by varying the gain of the amplification modules and tracking the output from the comparators on the signal channels. The photoelectric control unit can then use operating margin values to automatically set the system gain and thereby adjust the sensitivity of the unit for optimum performance.

Claims

1. A photoelectric detection system, comprising:

a microprocessor control unit;

a light source connected to said control unit for generating light pulses;

a photodetector arranged for detecting return light pulses originating with said light source and providing a photodetector output signal;

a first variable-gain amplifier module for amplifying said output signal from said photodetector in accordance with gain settings provided by said control unit to generate a main output signal;

a second variable-gain amplifier module for amplifying said main output signal from said first variable-gain amplifier module in accordance with gain settings provided by said control unit to generate a margin output signal; and

comparison means for comparing said main output signal from said first amplifier module and said margin output signal from said second amplifier module with a common reference level in order to generate comparison signals for supply to said control unit in order to allow said control unit to determine operating margin levels based on the gain settings furnished by said control unit to said amplifier modules.

2. The photoelectric detection system of claim 1, wherein said first amplifier module and said second amplifier module each include a fixed gain amplifier and a multiplying digital-to-analog converter operating as an attenuator under the control of said control unit for adjusting gain levels.

3. The photoelectric detection system of claim 1, wherein said microprocessor control unit includes a memory module having a software program resident therein for determining operating margin by manipulating the gain settings of said variable-gain amplifier modules and using said comparison signals to identify resulting output levels.

4. The photoelectric detection system of claim 1, wherein said light source includes a light emitting diode and said photodetector includes a photodiode.

5. A photoelectric detection system, comprising:

a light source for generating light pulses which are directed across a target range in which target objects may be present or absent;

a photodetector for detecting return light pulses from said target range and providing a photodetector output signal as a function of the presence or absence of said pulses which is indicative of the presence or absence of target objects in said target range;

a first amplification channel for amplifying said output signal from said photodetector and comparing this signal to a reference level to generate a pulse detection signal;

a second variable-gain amplification channel for amplifying said output signal from said photodetector and comparing this signal to a reference level to generate a margin level identification signal; and

control means for varying the gain of said second channel and tracking said pulse detection and margin level identification signals in order to determine operating margin.

6. The photoelectric detection system of claim 5, further including a main variable-gain module for amplifying said photodetector output signal prior to its supply to said first and second channels and wherein said control means is adapted for varying the gain of said main variable-gain module whereby gain levels on said channels can be throttled down.

7. The photoelectric detection system of claim 5, wherein said second amplification channel includes:

a first attenuator under control of said control means for varying gain,

a first fixed gain amplifier,

a comparator for comparing the output signal from said first fixed gain amplifier with a reference level.

8. The photoelectric detection system of claim 7, wherein said attenuator comprises a multiplying digital-to-analog converter and said control means comprises a microprocessor system operating under software control.

9. In a photoelectric detection system in which light pulses from a light source are periodically transmitted across a target range for synchronous detection by a photodetector in order to produce detection signals which can be amplified by a variable gain amplification module and thereafter used in providing an indication of the presence or absence of target objects in the target range, a method of automatically setting an optimum gain setting for said amplification module comprising the

generating a first detection signal with said photoelectric system under background conditions;

decrementing the gain of said amplification module until the operating margin for said system reaches a fixed OFF margin threshold;

generating a second detection signal with said photoelectric system under target conditions;

comparing the initial operating margin for said system under target conditions with a fixed ON margin threshold; and

setting said gain setting to the current gain level of said amplification module if the initial operating margin exceeds said ON margin threshold.

10. The photoelectric detection system of claim 9, further including the steps of:

incrementing the gain of said amplification module until the operating margin for said system reaches said ON margin threshold if the initial operating margin for said system does not exceed said ON margin threshold; and

setting said gain setting to an optimum value based on the gain of said amplification system at which said OFF margin threshold is reached and at which said ON margin threshold is reached.

11. The photoelectric detection system of claim 10, wherein said optimum value is calculated in accordance with the equation:

space="preserve" listing-type="equation">optimum gain setting =(2 * gain1 * gain3)/((2 * gain3) +(off margin * gain1))

Where;

Gain1=gain needed to get the ON operating margin up to 2.0 under target conditions

Off margin =minimum OFF operating margin measured during the under background conditions

Gain3 =gain at which the 0.3 OFF operating margin was produced under background conditions

12. The photoelectric detection system of claim 9, wherein said steps of incrementing and decrementing gain are performed by regulating the attenuation provided by one or more multiplying digital-to-analog converters.