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The analog inputs and outputs are one word long, so the address must start from an even byte, with an accuracy of 12 bits and an analog value of 0-32000.
Format: AIW [start byte address] AIW6;
AQW [start byte address] AQW0
Each analog input module is fixed in the order of the modules, and the order is backward. Example: AIW0 AIW2 ​​AIW4 AIW6 Each analog output module occupies two channels. Even if the first module has only one output AQW0 (EM235 has only one analog output), the second module analog output address should be addressed from AQW4. So on and so forth. (Note: The starting address of each module can be read online in plc/Information in step7 micro/win).
2. How do I connect the sensor to the S7-200 analog input module (EM231, EM235) and what are the precautions?
The analog input module can be set to different measurement methods by the DIP switch. The settings of the switch are applied to the entire module, and one module can only be set to one measurement range. (Note: The switch setting will not take effect until it is powered back on)
The input impedance is related to the connection: for voltage measurement, the input is 10 MOhm for high impedance; for current measurement, Rx and x need to be shorted and the impedance is reduced to 250 Ohm.
note:
In order to avoid the common mode voltage, the M terminal must be connected to the negative terminal of all signals, and the channel without the sensor should be shorted.
To prevent shorting of the analog module, a 750 Ohm resistor can be connected to the sensor. It will be connected in series with an internal 250 Ohm resistor and will guarantee current below 32 m A.
note:
If you use a 4-20 mA sensor, the measured value must be programmed to convert accordingly.
Input conversion: X=32000 *(AIWx – 6400) /(32000 – 6400)
Output conversion: Y = calculated value * (32000 – 6400) / 32000 + 6400
3. Why did you receive a very variable and unstable value when using the S7-200 analog input module?
1. You may have used a self-powered or isolated sensor power supply that is not connected to each other. This will produce a high common-mode voltage that vibrates up and down, affecting the analog input value.
2. Another reason may be that the analog input module wiring is too long or the insulation is not good.
Remedy:
1. Connect the negative terminal of the sensor input to the common M terminal on the module to compensate for such fluctuations.
note:
Be sure to make sure that this is the only connection between the two power supplies. If another connection already exists, an additional compensation current may be generated when the public connection is added.
background:
Analog input modules are not internally isolated.
The common mode voltage cannot be greater than 12V.
40dB for common mode interference of 60Hz
2. Use an analog input filter:
Go to "View > System block> Tab: Analog Input Filters" in Micro/Win.
Select analog input filter.
Select "Number of samples" and "Deadband".
The "Number of samples" area contains the values ​​calculated from the average of several samples. The value is calculated from the N sample values ​​that have been used in the past, and N is "Number of samples".
Deadband defines the maximum allowed to deviate from the mean
4. Why does the received signal change slowly when using the S7-200 analog input module?
Since you are using a filter, you can reduce the number of filtered samples or cancel the analog filtering in View > System block > Tab: Analog Input Filters.
5, EM231 RTD (thermal resistance) module wiring
For detailed wiring and DIP switch settings of the EM231 RTD module, please refer to Appendix A in the S7-200 System Manual.
Why is the SF red light on the EM231 RTD module FAQ module flashing?
There are two reasons why the SF red light flashes: the internal software of the module detects an external thermal resistance disconnection, or the input is out of range. Since the above detection is shared by the two input channels, the SF lamp must blink when only one channel is externally connected to the thermal resistor. The solution is to connect a 100 Ohm resistor to the empty channel in the same way as the used channel.
What is forward calibration and negative calibration?
The forward calibration value is 3276.7 degrees (Fahrenheit or Celsius) and the negative calibration value is -3276.8 degrees. If a wire break is detected and the input is out of range, the value of the corresponding channel is automatically set to the above calibration value.
The technical parameters of the thermal resistance are not very clear. How to set the type on the DIP switch?
The parameters of the thermal resistance should be removed as much as possible. Otherwise you can use the default settings.
note
The analog channel occupied by the EM231 RTD module should disable the filtering function when setting the analog channel filtering in the system block.
6. Can EM235 be used for RTD temperature measurement?
The EM235 is not a module for measuring the temperature connected to a thermal resistor, and it is easy to cause a malfunction. The EM231 RTD module is highly recommended.
7, EM231 TC (thermocouple) module frequently asked questions
Does the EM231 TC (thermocouple) module support type B thermocouples?
The EM231 TC supports J, K, E, N, S, T and R type thermocouples and does not support Type B thermocouples.
Does the EM231 TC need to compensate the wire?
The EM231 TC can be set to implement cold junction compensation by the module, but still requires compensation for the free end compensation of the thermocouple.
Why does the SF lamp of the EM231 TC module flash?
If wire break detection is selected, it may be broken. Short unused channels should be shorted.
Input out of range