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Data acquisition system data bus optical isolation


Board machine, microcontroller, and the emergence of the popularity of computer, making data acquisition system capable of dealing with the B power. So. The current data collection system with a computer are universally applied. Typical data acquisition system module structure shown in Figure 1. Map sensor and measuring circuit, also known as pre-circuit,[link widoczny dla zalogowanych], its role is to test multiple objects of physical signals into electrical data taken 1 scoop L signal skid system module structure, and set fire to a range of standard signal d door: analog / digital converter (A / B) price is more expensive, require complex circuitry, and a data acquisition system set the amount to be collected a lot, so take a multi-way switch, during data collection, each time to switch on all the way pass, the analog-digital conversion module into the module into a digital number. Diagram control circuit module can be used to control the dynamic characteristics of the front circuit to control multiple switches and analog-digital conversion of the synchronization and start and stop. Analog into a digital number stored in the computer, data processing, data acquisition to be completed so that the whole process. Common data acquisition system can measure the amount of many different types of devices connected to the ever-changing, plus the use environment is very complex and will bring all kinds of interference to the system, if there is a good investment approach, the light loss of measurement accuracy will be serious When the data collected can not response was' clam object property 994-0s 23 Received a ten 28 years old male cut school to one the 6 Yao Danya, etc.; data mining as the optical system ll_ fallen from the data line management characteristics,[link widoczny dla zalogowanych], thus eliminating the interference measurement data acquisition system is designed to be considered an important aspect. Affect the accuracy of the data acquisition system in the interference mainly from two sources, the first field application of the complex environment of the interference signal, which the circuit through the sensor and the additional strings into the data acquisition system, people generally use this type of interference filter and other means, and has been discussed more articles on this no details. The other is the data acquisition system internally generated. Il 『on to the computer power supply used in many chips as the switching power supply, - the quality is not good, the current set circuit (including A / D conversion circuit) and computer circuits share power, often lead to high frequency interference signals ripple pre-circuit, the ripple value to tens of millivolts can often greatly reduce the accuracy of the data acquisition system. Another way the computer I need a high frequency signal as a synchronization clock (usually two megabytes to tens of megabytes), which also have high-frequency interference, which might affect measurement accuracy. Of this type of interference signal, the use of optical isolation measures can eliminate its influence, the conventional approach is to add digital to analog conversion circuit after optical isolation circuit. A / D conversion by the data, control circuit and front A / D conversion of the signals and pre-existing buffer status signals, transmitted through the photoelectric conversion, shown in Figure 2. This method is less demanding on the photoelectric conversion rate, the low-speed data acquisition system,[link widoczny dla zalogowanych], which is a high performance and low cost method】 species. Front entombment 2 iliac hide the low-speed optical isolation with a computer buffer but in the special requirements of data acquisition systems, computer parts and the connection between the front circuit is more complex, not only have to pass between them one-way direction of the signal line and control lines, as well as the direction of two-way data transfer bus. Rate of change of data bus is much faster than the measured signal, the signal sent in both directions for several _ oak bus shown in Figure 3 the principle of isolation. Muscle set. Meter circuit, and} l Figure 3 of the data bus from the 'because the direction of a single photoelectric conversion, so the data lines are required every two optical isolator, in order to control the direction of data transfer direction control lines needed. The circuit shown in Figure 3, the use of read and write data bus to allow the direction of signal control. When the computer to write when the write enable signal effectively, A bus data to the front compartment by light circuit, when the computer read operation, read enable signal valid, pre-B light separated by the circuit data to the computer. Computer read / write timing is shown in Figure 4,[link widoczny dla zalogowanych], the data bus effectively withdraw pat ? b: - b = b j ---- <--------)---- try a bar - a 4 computer literacy indiscriminately when asked about the timing to make a few hundred nanoseconds, the time to read and write effectively removed the small number of effective time z shorter than that. The commonly used optical coupling device has two classes, one for the ordinary, a class of high-speed type. Common type of light response time across a number of microseconds, it is clear from the resistance can not be used on the bus, and high-speed optical compartment (such as 6N137) response time of tens of nanoseconds, which can basically meet the need. Optocoupler response time interval 6Nl37 test circuit shown in Figure 5tDHL and tpL much 75ns. Entropy = _ one in Figure 5 separated 6N137 optocoupler guillotine test circuit response time bi-directional data bus isolation circuit should be hanging in the l, to obtain satisfactory results.

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