Opto-electronic Interfaces
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SL MA-110 Optical Transmittance Analyzer
(Standard all-purpose interface)
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SL MA-100/110 opto-electronic interfaces showing optical transmitter/receiver receptacles (left) and electrical screw clips (right).
Small dynamic (AC-coupled) interface device in plastic module housing. Can also be used for simple static (DC) measurements. Internal Schmitt-Trigger with light-level-controlled threshold enables sensor-independent trigger sensitivity. Internal failure detection to indicate out-of-range conditions (e.g. torn fiber) by a particular output signal. Optocoupler outputs for trigger and failure signals. Short-circuit-protected analog signal outputs. Reverse power protection. No adjustment necessary. Powerful IRED transmitter (Laser Class 3A when fiber disconnected). Suitable for feeder lengths up to 250m.
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Typical signals as produced by a passenger car with front motor at about 60 km/h (37 mph). Test equipment: SPZ fiber optic axle sensor with SL MA-110 optical transmittance analyzer. Upper: Load dependent analog voltage, lower: digital trigger signal.
The SL MA-110 is an interface ideally suited for all common axle detection, axle counting and speed measuring purposes, but also a convenient means to e.g. simply feed light into an optical fiber or measure light emerging from a fiber. It is designed in a way that it can easily be configured to meet a maximum number of custom requirements as well as extended by supplementary circuits for additional functionality.
The MA-110 is able to feed a variable amount of light into the fiber thus adapting to large variations of the sensor and feeder transmittance. Therefore its analog signals are no linear functions of the transmittance. Also its power consumption is not constant. The more light is needed the more current is required to provide it. Thus, under normal conditions the MA-110's supply current remains considerably below its maximum value of 100mA.
For special purposes the MA-110's predecessor MA-100 – which does not have this adaptive behaviour but linear signals instead – can still be made available on request.
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The SL MA-110 DT Static Version
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The MA-110 interface can be modified in a special way which allows simple measurement of the transmitted light without any signal processing and also without AC coupling. The variable feeding of light into the sensor is maintained so the full dynamic range of the MA-110 is still covered. As a consequence of the special circuitry this kind of interface can not be overdriven, neither by sensor transmittance nor by the load signal. It is therefore specially suited for all applications which require processing of the raw analog signal.
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SL MA-310 Optical Transmittance Analyzer
(Dynamic 3-channel interface)
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The SL MA-310 three Channel Optical Transmittance Analyzer (OTA) is an electronic interface that operates three fiber optic load sensors. The SL MA-310 serves as the interface between the fiber optic sensor and the processing unit on system level. It should be installed in a weatherproofed road side cabinet.
The interface responds to the optical sensor signal in a dynamic (AC-coupled) manner, i.e. the electrical signal caused when a load is applied to the sensor decreases to zero as the load remains applied. At a tuneable threshold, a digital trigger signal per channel is generated. This signal is automatically reset after an adjustable time period.
These characteristics allow the SL MA-310 interface to operate without the need for adjustment.
If the interface detects an interruption in the light transmission path of any channels, it flashes a particular light for each interrupted channel. The output signals (trigger signals) are transmitted via optocouplers which behave similar to relays, allowing the use of a variety of output circuitry.
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SL MD-220 Optical Transmittance Analyzer
(Static 2-channel interface)
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SL MD-220 two-channel static (DC-coupled) opto-electronic interface
With its advanced circuitry, this static (DC-coupled) interface can detect a load on a sensor for as long as it is applied to the sensor. It comes as a 120x100 mm printed circuit board.
The MD-220 incorporates a TI MSP-430 embedded microcontroller, programmable via a JTAG interface. It has a 10-wire screw-clip interface with power supply terminals and four floating optocoupler outputs. It also has a RS-232 interface for input and output of data. Direct external control is possible through the use of one 8-way SIL switch, two jumpers and a reset switch. For quick troubleshooting, six status display LEDs show the function of the interface and there are five easily accessible test points for analog measurements.
Power consumption has been minimized by circuitry that operates the transmitter diodes in series while independently controlling the current through each diode. The MD-220 comes with two different kinds of transmitter diodes, a near infrared diode giving each channel a dynamic range of 30 dB and a more economic visible light diode for a dynamic range of 20 dB.
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