Both Mitsubishi and Siemens' plc have their own unique advantages. Let's talk about the Mitsubishi 2AD module. The 2AD module provides a 12-bit resolution module. The maximum number of digits is 4096. How is this 4096 and 12-bit resolution? A 12-value 1 of a relational binary is 4096. Of course, the maximum digital 4096 is adjustable by the gain potentiometer on the 2AD module.
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I take a PT100 200 degree temperature sensor as an example. The analog current of 0 degree corresponding to this sensor is 4mA. The corresponding analog current is 20mA. The first step is to calibrate the gain and offset of 2AD. The gain and offset are actually the digital quantities corresponding to the analog currents of 4mA and 20mA. We take a current generator to generate a 20mA current and then connect it to the 2AD analog current input. After the PLC is powered on, find the data register corresponding to the analog quantity to see what the current value is. The data inside may be an unknown data. This is because 2AD is not adjusted to a standard when it leaves the factory. We adjust the gain potentiometer. Let the number of 4000 be 4000, why should we adjust to 4000? Because the temperature sensor has a range of 200 degrees, they happen to be a 20-fold relationship. The next step is to offset, adjust the current generator output 4mA current, it depends on the number of digital registers in the data register. If the digital value of the data register is 0 then we do not need to adjust. After the gain and offset are adjusted, the actual detection of the sensor is connected. The program in the PLC uses the division instruction, because dividing the data in the data register by 20 is the actual temperature. Of course, this is not enough because of many automation controls. Occasionally, the temperature must be very accurate, so the floating point number conversion instruction and the floating point number division instruction are used. Mitsubishi's floating point number can retain 3 digits after the decimal place, that is, 0.000 degrees.
It is important to note that the above is the ability to complete the analog function, but the temperature change we see is very fast, because the PLC performs an analog acquisition and analog calculation every scan cycle. This time is very fast. It is usually executed once every 20ms, so the number change inside is very fast. In this case, we need the average value. The specific method is to use the accumulating instruction to divide the accumulated data by the accumulated number of times. The total number of accumulations is between 5 and 10 times.
The analog quantity of Siemens is different from that of Mitsubishi. His resolution is higher than that of Mitsubishi. The Siemens EM231 is a module that provides a 16-bit resolution. The maximum digital quantity is 32000, which is the capacity of a word. The analog quantity of Siemens is also different from Mitsubishi in terms of usage. Because Siemens does not have gain and offset adjustment potentiometers, all corresponding digital quantities are calculated by the formula. However, the Siemens program is modular, and the programming is much simpler. The raw data can be obtained directly in the AIW data register.
I will simply talk about a 200-degree sensor. The analog current output from this sensor is 4 to 20 mA. The digital quantity of Siemens is 0 to 32000. If you follow the Mitsubishi algorithm, it will go wrong, because 4 mA is not the corresponding digital quantity. 6400, because they are 1600 times the relationship, 4mA multiplied by 1600 = 6400, so we have to find a coefficient of the number 6400 and 32000 and temperature 200, the specific formula is this (32000-6400) divided by 200 = 128. This 128 is their coefficient, divided by 400 if the temperature sensor is 400 degrees.
Finally, we divide the data in the AIW data register by 128 to the current temperature. It is worth noting that the analog of Siemens is best in the interrupt program. 
