OIS25
11Pages

OIS25Optical smart sensor for hydraulic cylinders General Description OIS25 is a patented smart optical device, which is usually combined with a hydraulic steering cylinder. The main application is on rough terrain machines, to detect when the wheels are correctly aligned. The alignment occurs when the sensor detects a different refraction index zone, which is marked on the hydraulic cylinder’s rod. The product is based on reflective sensor as input stage, a computing unit (microprocessor device) and an output stage with high side driver, which is able to deliver up to 150mA. The sensor includes a lot of “smart” functions and special algorithms that allow to continuously adapt the device to the wear of the system during the time, improve the life of the system, guarantee the high reliability (MTTF =103 years at 24 V) and be able to work in the harsh environment (temperature variations, rod wear, presence of electromagnetic disturbs, presence of humidity, shocks and vibrations). In addition, the particularity of this serie is that it provides diagnostic functions to auto detect possible failures. At every bootup the OIS25 is able to collect information about the functioning of the logic unit, of the output stage and of the sensor module. Applications Steering machines Surface cleaning machines Rough terrain machines Road building machines Construction machines Features ■ Especially designed for earth moving environment ■ Diagnostic functions onboard ■ MTTF = 103 years @ 24V ■ Meets all ISO 7637-2 and ISO16750-2 requirements, including Load Dump at max levels ■ Smart interface and smart algorithm ■ High input voltage range ■ High temperature range ■ High current output ■ IP67 ■ Inversion of polarity protection ■ Overload protection Agricultural machines Logistic machines Loaders Function Power Supply Ground Output (PNP) Cable color Name Brown Vcc Black GND Grey OUT Ordering Information OIS25-DT-CE03 With a 60cm cable + DT04-3P-CE03

ABSOLUTE MAXIMUM RATINGS

OIS25 MECHANICAL DIMENSIONS The dimensions are expressed in mm, tolerance ±0.1mm. Figure 1 – Right angle versions OUTPUT CONFIGURATION

Table 1 - Compliance table f Load Dump pulse and Cranking pulse only.

OIS25 Application circuits _________________________________________________________________Resistive load A typical output load is a lamp. For such resistive loads no precautions shall be taken: the output stage is protected against reverse of polarity, short circuit and temperature. The power absorbed by the output stage is equal to RDSON * Iload. Figure 3 – Resistive load connection and VOUT transition graph Inductive load_________________________________________________________________ Inductive loads are described by inductance L and resistance R. At switch ON, the inductive load...

In this case, depending on the supply voltage and on the time constant, there is a real risk to break the output stage of the sensor. The output stage is composed of a logic stage, a power mosfet and a zener diode: the diode protects the output against overvoltages. If the VDS of the output stage during the transitory becomes very high (double the Vcc value) for long period, it can destroy the mosfet or the zener protection diode inside the output stage. In order to avoid this possible situation, the use of a freewheeling diode in parallel to the load is recommended. Figure 6 - VOUT...

Load dump means the disconnection of a powered load. It can cause large voltage spikes from the inductive generator(s). In automotive electronics, it refers to the disconnection of the vehicle battery from the alternator while the battery is being charged. Due to such a disconnection of the battery, other loads connected to the alternator see a surge in power line. Load dump may occur as a result of cable corrosion, poor connection or of intentional disconnection with the engine running. The pulse shape and parameters for an alternator with no centralized load dump suppression (Chap. 4.6.4...

Diagnostic At the boot-up, the sensor enters automatically in diagnostic mode and, for the first 2.2 s the OUT pin is used as signalling output. The implemented features are able to diagnose the functioning of: • the logic unit • the output stage • the sensor module. In case of failure of at least one of this functions, the sensor stops working and the results of the diagnostic functions are stored in EEPROM (the EEPROM can be read only by the producer). Logic Diagnostics Output Diagnostics Sensor Diagnostics Figure 8 - Diagnostic flow chart Note: it is important to avoid the shut...

Figure 9 – Diagnostic signal Figure 10 – Diagnostic signal – Oscilloscope

LOGIC UNIT The sensor uses the EEPROM memory embedded in the microcontroller to save some functional parameters. The most important parameter is the gain value of the optical sensor which is set during the calibration phase. To ensure the consistency of the data, the gain value is combined with a 5 bytes hex code and the sequence so obtained is processed to calculate the CRC-8 value (CCITT polynomial). Figure 11 - EEPROM structure At every boot-up, the sensor reads from EEPROM the gain value and the 5 bytes code, re-calculates the CRC-8 value and compares it with the CRC-8 value stored in...

Figure 12 shows the output stage diagnostic and the time duration of one (left) and five (right) transitions. Figure 12 – Output stage diagnostic detail – Oscilloscope SENSOR MODULE The sensor module is represented by a light emitting diode, a photo receiver and an amplifier. The functioning of the input stage is tested analyzing the sensor response with different gain values. Thanks to a special algorithm, based on gain variations, it is possible to test the correct functioning of every component. If one of them does not respond as expected, a sensor module failure is reported.