Most customers encounter various problems when using analog input modules. Of course, the most common feedback we receive from customers is also about the application of analog input modules. Today, I'll share some common problems with you.
1. How are the UN-200 analog input modules EM231 and EM235 addressed?
The analog input and output are one word long, so the address must start with an even number of bytes, with a precision of 12 bits, and the analog value is a number from 0 to 32000.
Format: AIW [Starting byte address] AIW0;
AQW [Starting byte address] AQW0
Each analog input module has a fixed address based on its order, arranged sequentially. For example: AIW0, AIW2, AIW4, AIW6. Each analog output module occupies two channels. Even if the first module only has one output AQW0 (EM235 only has one analog output), the address of the second module's analog output should start from AQW4, and so on. (Note: The starting address of each module can be read online in Step7 Micro/Win's PLC/Information section).
2. How to connect the sensor to the S7-200 analog input module (EM231, EM235) and what precautions should be taken?
Here's a wiring diagram for your reference:
The analog input module can be configured with different measurement methods via DIP switches. The switch settings apply to the entire module, and a module can only be configured with one measurement range at a time. (Note: Switch settings only take effect after a power cycle.)
3. Input impedance is related to connection: When measuring voltage, the input impedance is high at 10 MOhm; when measuring current, Rx and x need to be shorted, and the impedance is reduced to 250 Ohm.
Notice:
To avoid common-mode voltage, the M terminal must be connected to all negative signal terminals, and channels without connected sensors must be shorted.
Notice:
If you are using a 4-20mA sensor, the measured values must be converted accordingly through programming.
Input transformation: X = 32000 * (AIWx – 6400) / (32000 – 6400)
Output conversion: Y = calculated value * (32000 – 6400) / 32000 + 6400
4. Why do I receive a highly fluctuating and unstable value when using the UN-200 analog input module?
1) You may be using a self-powered or isolated sensor power supply, and the two power supplies are not connected to each other. This will generate a high common-mode voltage with fluctuating voltage, affecting the analog input value.
2) Another reason may be that the wiring of the analog input module is too long or the insulation is poor.
Remedial measures:
a. Connect the negative terminal of the sensor input to the common M terminal on the module to compensate for this fluctuation.
Notice:
It is essential to ensure beforehand that this is the only connection between the two power sources. If another connection already exists, adding a common connection may result in an unnecessary compensating current.
in accordance with:
Analog input modules are not internally isolated (e.g., 8AI).
The common-mode voltage must not exceed 12V.
The common-mode interference at 60Hz is 40dB.
b. Using an analog input filter:
In Microsoft Windows, navigate to "View > System block > Tab: Analog Input Filters".
Select analog input filtering.
Select "Number of samples" and "Deadband".
The "Number of samples" field contains a value calculated from the average of several samples. This value is calculated using N existing sample values, where N is the "Number of samples".
The deadband defines the maximum deviation from the average that is allowed.
5. Why does the received signal change very slowly when using the S7-200 analog input module?
Since you used a filter, you can reduce the number of filtered samples or disable analog filtering in View > System block > Tab: Analog Input Filters.
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