1: In what environment is Step7 Micro/WIN V4.0 installed?

Step7 Micro/WIN V4.0 installation and operating environment:

Windows 2000 SP3 and above

Windows XP Home

Windows XP Professional

Siemens does not test under other operating systems and does not guarantee its use.

2: How compatible is Step7 Micro/WIN V4.0 and other versions?

Project files generated by Micro/WIN V4.0. Old versions of Micro/WIN cannot be opened or uploaded.

3: What is the difference between the siemens200 PLC hardware version?

The second generation S7-200 (CPU22x) series is also divided into several major hardware versions.

The 6ES721x-xxx21-xxxx is the 21st edition; the 6ES721x-xxx22-xxxx is the 22nd edition.

Compared with version 21, version 22 has improved hardware and software. The 22 version is downwardly compatible with the 21 version feature.

The main difference between 22 and 21 is:

The free port communication rate of the 21st edition CPU 300, 600 is replaced by 22 edition 57600, 115200, 22 editions no longer support 300 and 600 baud rate, 22 editions no longer have the restriction of the location of the intelligent module

4: plc power change how to connect?

In the power supply wiring to the CPU, we must be very careful to distinguish what kind of power supply, if the 220VAC is connected to the 24VDC power supply CPU, or accidentally received 24VDC sensor output power, will cause the CPU to damage.

5:200PLC processor is how many?

The central processing chip of the S7-200 CPU has a 32-bit data length. The data length of the CPU accumulator AC0/AC1/AC2/AC3 can also be seen.

6: How to perform the power requirement and calculation of S7-200?

The S7-200 CPU module provides 5VDC and 24VDC power supplies:

When there is an expansion module, the CPU provides 5V power through the I/O bus. The sum of the 5V power consumption of all expansion modules cannot exceed the power rating provided by the CPU. If not enough can not use external 5V power supply.

Each CPU has a 24VDC sensor power supply that provides 24VDC for the local input point and expansion module input points and expansion module relay coils. If the power requirement exceeds the power rating of the CPU module, you can add an external 24VDC power supply to the expansion module.

The so-called power supply calculation is to use the power supply capacity that the CPU can provide, minus the power consumption required by each module.

note:

The EM277 module itself does not require a 24VDC power supply. This power supply is dedicated to the communication port. The 24VDC power requirement depends on the load on the communication port.

The communication port on the CPU can connect the PC/PPI cable and the TD 200 and supply them with power. This power consumption is no longer included in the calculation.

7:200 PLC can work at minus 20 degrees?

The working environment requirements of the S7-200 are:

0°C-55°C, horizontal installation

0°C-45°C, vertical installation

Relative humidity 95%, no condensation

Siemens also offers the S7-200 wide temperature range product (SIPLUS S7-200):

Operating temperature range: -25°C-+70°C

Relative humidity: 98% at 55°C, 45% at 70°C

Other parameters are the same as those of ordinary S7-200 products

S7-200 wide temperature products, each with its own order number, can be found on the SIPLUS product homepage. If not found, there is no corresponding SIPLUS product.

There is no wide temperature type product for text and graphic display panels.

Also note that there is no spot in the country. Please contact your local Siemens office or distributor if you need to.

8: How fast is the digital input/output (DI/DO) response speed? Can I make high-speed input and output?

The S7-200 has a hardware circuit (chip, etc.) on the CPU unit to handle high-speed digital I/O, such as high-speed counter (input), high-speed pulse output. These hardware circuits work under the control of the user program and can reach very high frequencies; however, the number of points is limited by hardware resources.

The S7-200 CPU works according to the following mechanism:

Read input point status to input image area

Execute the user program, perform logical operation, and get the new state of the output signal

Write output signal to output image area

As long as the CPU is in operation, the above steps are performed over and over again. In the second step, the CPU also performs communications, self-checks, and other tasks.

The above three steps are the software processing of the S7-200 CPU and can be considered as the program scan time.

In fact, the S7-200's speed of digital processing is limited by the following factors:

Input hardware delay (from the moment the state of the input signal changes, to when the CPU refreshes the input image area)

CPU internal processing time, including:

Read input point status to input image area

Execute the user program, perform logical operation, and get the new state of the output signal

Write output signal to output image area

Output hardware delay (the time from the output buffer status change to the actual level change at the output point)

The above three periods of A, B, and C are the main factors that limit the PLC's ability to process the digital response speed.

A practical system may also need to consider input and output device delays, such as the output relay external relay operating time

Table 1. Input Point Hardware Delays

The above data are all indicated in the "S7-200 System Manual". Here is a list comparison. The time delay (filter) time of some input points on the CPU can be set in the "system block" of the programming software Micro/WIN. The default filter time is 6.4ms.

If the vulnerable signal is connected to the DI point on the CPU that can change the filter time, adjusting the filter time may improve the signal detection quality.

Input points that support the high-speed counter function are not constrained by this filter time when the corresponding function is turned on. The filter setting is also effective for refreshing the input image area, digital input interruption, and pulse catching functions.

Table 2. CPU Output Hardware Delays

Some output points are faster than others because they can be used for high-speed output functions and have special design in hardware. When the hardware high-speed output function is not used exclusively, they are treated just like ordinary points.

The relay output switching frequency is 1Hz.

Table 3. Extension Module Output Hardware Delays

9: What are the countermeasures for the S7-200 to handle fast response signals?

Using the CPU's built-in high-speed counter and high-speed pulse generator to process sequential pulse signals

The hardware interrupt function using some CPU digital input points is handled in the interrupt service routine; the delay to enter the interrupt can be ignored

The S7-200 has direct read input and direct write output instructions that can override the time limit of the program scan cycle

Capture a short pulse using the "Pulse capture" function of the partial CPU digital input

Note: The minimum periodic timing task in the S7-200 system is 1ms.

All measures to achieve rapid signal processing must consider the impact of all limiting factors. For example, it is obviously unreasonable to choose a hardware with a 500μs output delay for a signal that requires a millisecond response speed.

10: Is the S7-200 program scan time related to program size?

The program scan time is proportional to the size of the user program.

The "S7-200 System Manual" has data on the execution time of each instruction. It is actually difficult to pre-calculate the program scan time in advance, especially if the program has not yet been programmed.

It can be seen that the conventional PLC processing mode is not suitable for digital signals requiring high time response. It may be necessary to use special methods depending on the specific task.

11: How fast can the CPU224 XP high-speed pulse output reach?

The CPU224 XP's high-speed pulse outputs Q0.0 and Q0.1 support frequencies up to 100KHz.

Q0.0 and Q0.1 support 5-24 VDC outputs. But they must be grouped together with Q0.2 - Q0.4 to output the same voltage. High speed output can only be used in CPU224 XP DC/DC/DC models

12: Is the analog input on the CPU 224 XP highly responsive?

Its response speed is 250ms, which is different from the data of the analog expansion module. The analog I/O chip on the CPU 224 XP is different from the one used on the analog module. The application has different conversion principles, so the accuracy and speed are different.

13: How does the address of the analog module hanging behind the CPU 224 XP be allocated?

The analog I/O address of the S7-200 is always increased by 2 channels/module. Therefore, the address of the first analog input channel behind the CPU 224 XP is AIW4; the address of the first output channel is AQW4, and AQW2 cannot be used.

14: What communication protocol does the communication port on the S7-200 CPU support?

1) PPI Protocol: The communication protocol developed by Siemens for S7-200

2) MPI protocol: not fully supported, only as a slave

3) Freeport mode: User-defined communication protocol used to communicate with other serial communication devices (such as serial printers, etc.).

The S7-200 programming software Micro/WIN provides the communication function realized through the free port mode:

1) USS command library: for S7-200 and Siemens drives (MM4 series, SINAMICS G110 and older MM3 series)

2) Modbus RTU command library: used to communicate with devices that support the Modbus RTU master protocol

The two communication ports on the S7-200 CPU are basically the same, and there is no special difference. They can each work in different modes and communication speeds; their mouth addresses can even be the same. Devices connected to the two communication ports on the CPU, respectively, do not belong to the same network. The S7-200 CPU cannot act as a bridge.

15: What are the communication ports on the S7-200 CPU?

1) programming computer with programming software Micro/WIN can program plc

2) The communication port that can be connected to other S7-200 CPUs forms a network

3) Can communicate with MPI communication port of S7-300/400

4) Siemens HMI devices can be connected (eg TD 200, TP170micro, TP170, TP270, etc.)

5) Data can be published via OPC Server (PC Access V1.0)

6) Can connect other serial communication equipment

7) Can communicate with third party HMI

16: Is the communication port on the S7-200 CPU extendable?

It is not possible to expand the communication port that is identical to the function of the CPU communication port.

If the communication port on the CPU is not enough, you can consider:

Buy a CPU with more communication ports

Consider the type of connected equipment. If there is a Siemens man-machine interface (HMI, operation panel), consider adding an EM 277 module and connecting the panel to the EM 277

17: How far is the communication distance from the communication port on the S7-200 CPU?

The data given in the “S7-200 System Manual” is a network segment of 50m, which is the communication distance that can be guaranteed under the compliant network conditions. Everywhere beyond 50m, repeaters should be added. Adding a repeater can extend the communication network by 50 meters. If you add a pair of repeaters, and there is no S7-200 CPU station between them (there can be EM277), the distance between the repeaters can reach 1000 meters. Meet the above requirements can be very reliable communication.

In fact, there are users who do more than 50m distance without repeater communication. Siemens cannot guarantee that such communications will be successful.

18: What factors should be taken into account when designing a network?

The communication port on the S7-200 CPU is electrically RS-485, and the RS-485 supports a distance of 1000m.

The communication port on the S7-200 CPU is non-isolated. Pay attention to ensure that the communication ports on the network are equal in potential.

Signal transmission conditions (network hardware such as cables, connectors, and external electromagnetic environment) have a great impact on the success of communications

19: Does the S7-200 have a real-time clock?

The CPU221 and CPU222 do not have a built-in real-time clock. External clock/battery cards are required to obtain this function. The CPU224, CPU226, and CPU226 XM have built-in real-time clocks.

20: How to set the date and time value so that it starts to move?

1) Using the programming command of the programming software (Micro/WIN) PLC > Time of Day Clock..., the clock starts to move after completion of the online connection with the CPU.

2) Edit the user program using the Set_RTC (Set Clock) instruction setting.

21: How is the address of the smart module allocated?

Apart from the digital and analog I/O expansion modules occupying the input/output addresses in the S7-200 system, some intelligent modules (special function modules) also need to occupy addresses in the address range. These data addresses are used by the module for functional control and are generally not directly connected to external signals.

CP243-2 (AS-Interface module) In addition to using IB/QB as status and control bytes, AI and AQ are used for address mapping of AS-Interface slaves.

Related images on this topic are as follows:

22: Step7 - How compatible is Micro/WIN?

Currently common Micro/WIN versions are V4.0 and V3.2. Older versions, such as V2.1, have no value for continued application except for converting old project files.

Different versions of Micro/WIN generate different project files. The higher versions of Micro/WIN are backwards compatible with project files generated by older versions of the software; lower versions of the software cannot open project files saved by higher versions. It is recommended that users always use the latest version. The latest version is currently Step7 - Micro/WIN V4.0 SP1.

23: How to set the communication port parameters?

By default, the communication interface of the S7-200 CPU is in PPI Slave mode, the address is 2, and the communication speed is 9.6K.

To change the address or communication speed of the communication port, you must set it in the Communicaiton Ports tab in the system block and then download the system block to the CPU for the new settings to take effect.

24: How to set the communication port parameters to improve the network performance?

Assume that stations 2 and 10 in a network are used as masters, and the highest address (of station 10) is set to 15. For station No. 2, the so-called address gap is a range of 3 to 9; for station No. 10, the address gap is a range of 11 to the highest site 15, and stations 0 and 1 are also included.

The tokens are transmitted between the master stations in the network communication, which separately controls the communication activities on the entire network. All masters on the network do not join the token transfer ring at the same time, so a master station that holds the token must periodically check to see if there is a new master added to the site higher than itself. The refresh factor refers to checking a high site once after the first few token acquisitions.

If the address gap factor of 3 is set for station 2, then when station 2 gets the token for the third time, an address in the address gap is checked to see if there is a new master station to join.

Setting a larger factor increases network performance (because of unnecessary site inspections), but it can affect the speed at which new hosts join. The following settings will improve the running performance of the network:

1) Set the highest address closest to the actual highest site

2) Keep all master station addresses in a row, so that no new master station detection in address gaps will occur.

25: How to set data retention function?

Data retention settings define how the CPU handles data retention tasks for each data area. What is selected in the data retention setting area is the data area whose data content is to be "held". The so-called "maintenance" means that after the CPU is powered off and then powered on, the contents of the data area remain in the state before the power was turned off. The data retention function set here is implemented in the following ways:

The data retention function set here depends on the built-in supercapacitor of the CPU. After the supercapacitor is discharged, if the external battery (or CPU221/222 clock/battery) card is installed, the battery card will continue powering the data retention. Until discharge data is automatically written into the corresponding EEPROM data area before power-off (if MB0 - MB13 are set to hold)

26: What is the relationship between data retention setting and EEPROM?

If the storage unit in the range of MB0 - MB13 total 14 bytes is set to "Hold", the CPU will automatically write its contents to the corresponding area of ​​the EEPROM when the power is turned off, and use the contents of the EEPROM after re-powering. Overwrite these storage areas

If the range of other data area is set to "not held", the CPU will copy the value in EEPROM to the corresponding address after re-power on.

If the data area range is set to "Keep", if the built-in super capacitor (+battery card) fails to retain data, the contents of the EEPROM will be overwritten with the corresponding data area, otherwise it will not be overwritten.

27: What kinds of passwords are set?

Set the CPU password in the system block to limit the user's access to the CPU. You can set passwords hierarchically and open different levels of permissions to other people.

28: After the CPU password is set, why can't I see that the password has taken effect?

After setting the CPU password in the system block and downloading it, because you still keep the Micro/WIN communication connection with the CPU, the CPU will not protect the Micro/WIN that sets the password.

To verify that the password is valid, you can:

1) Stop communication between Micro/WIN and CPU for more than one minute

2) Close the Micro/WIN program and open it again

3) Stop the CPU's power supply and send power again

29: Does the digital/analog have a freeze function?

The digital/analog output table specifies how the digital output or analog output channel operates when the CPU is in the STOP state.

This function is very important for some equipment that must keep moving and running. If the brake, or some key valves, etc., are not allowed to stop when the PLC is commissioned, it must be set in the output table of the system block.

Digital quantity: After “Freeze output in last state” is selected, the last state is frozen, and the digital output point remains in the state before shutdown when the CPU enters the STOP status (Yes is still 1 and 0 is kept as 0). The following b. table does not work If unchecked, then the selected output point will remain ON (1) state, unchecked is 0.

Analog quantity: After selecting “Freeze output in last state”, the last state is frozen, then the analog output channel remains in the state before shutdown when the CPU enters the STOP state, and the following table does not work. When not selected, the following Each table specifies the output value of the analog output channel when the CPU enters the STOP state.

30: What is the role of digital input filter, how to set it?

You can select different input filter times for the digital inputs on the CPU. If the input signal has interference or noise, adjust the input filter time and filter out the interference so as to avoid malfunction. The filter time can be selected in the range of 0.20 ~ 12.8ms. If the filter time is set to 6.40ms and the active level (high or low) of the digital input signal lasts less than 6.4ms, the CPU will ignore it; only if the duration is longer than 6.4ms, it will be possible to identify.

In addition: Input points that support the high-speed counter function are not constrained by this filter time when the corresponding function is turned on. The filter settings are effective for refreshing the input image area, digital input interruption, and pulse capture functions.

31: What effect does the analog filter have?

In general, the S7-200's analog filtering function eliminates the need for additional user filtering programs.

If an analog filter is selected for a channel, the CPU will automatically read the analog input value before each program scan cycle. This value is the filtered value and is the average of the set number of samples. The analog parameter settings (number of samples and deadband value) are valid for all analog signal input channels.

If a channel is not filtered, the CPU will not read the average filter value at the beginning of the program scan cycle, but will only read the actual value at the time when the user program accesses the analog channel.

32: How to set the deadband value of analog filter?

Dead-band value, which defines the range of values ​​for calculating the average value of the analog

If the sampled value is within this range, the average value set by the sample number is calculated; if the current sampled value exceeds the upper or lower limit of the dead zone, the value is immediately adopted as the current new value, and as a later The starting value of the average calculation

This allows the filter to have a fast response to large changes in analog values. The deadband value is set to 0, which means that the deadband function is disabled, ie all values ​​are averaged regardless of how much the value changes. For fast response requirements, do not set the deadband value to 0 and set it to the maximum permissible disturbance value (320 is 1% of full scale 32000)

33: What should be noticed in the setting of analog filtering?

1) Select filter for slower changing analog input to suppress fluctuations

2) Selecting a smaller number of samples and dead zone values ​​for faster changing analog input will speed up the response

3) Do not use filters for high-speed changing analog values

4) Filters cannot be used if analog signals are used to transfer digital signals, or when using RTD (EM231 RTD), thermocouple (EM231 TC), AS-Interface (CP243-2) modules

34: How to make the monitoring response in Micro/WIN faster?

The background communication time can be set. The background communication time defines the percentage of communication time of Micro/WIN and CPU used for “operating mode programming” and program/data monitoring as the percentage of the entire program scan cycle. Increasing this time can increase the communication opportunities for monitoring. The response in Micro/WIN will feel faster, but it will also increase the program scan time.

35: The indicator on the CPU can be customized?

The user can customize the indicator light

The 23 CPU's LED indicator (SF/DIAG) can display two colors (red/yellow). Red indicates SF (system failure), yellow DIAG indicator can be customized by the user.

Custom LED indicators can be controlled by the following methods:

1) Set in the Configuration LED tab of the system block

2) Use the DIAG_LED instruction in the user program to light up

The above conditions are the relationship between or. If both SF and DIAG instructions appear, the red and yellow lights flash alternately.

36: Can I use the entire program memory at any time?

The new features of the CPU version 23 (runtime programming) require a portion of the program memory space. If you want to use the entire program memory area, the "Run Mode Programming" function needs to be disabled for certain CPU models.

37: If I forgot my password, how do I access a CPU with a password?

Even if the CPU is password protected, you can use the following features without restriction:

1) Read and write user data

2) Start and stop the CPU

3) Read and set the real-time clock

If you do not know the password, the user cannot read or modify the program in a CPU with a three-level password protection.

38: How to clear the set password?

If you don't know the CPU password, you must clear the CPU memory before you can download the program again. Executing a clear CPU instruction does not change the CPU's original network address, baud rate, and real-time clock; if there is an extra program memory card, its contents will not change. After the password is cleared, the original program in the CPU will not exist.

To clear the password, follow the steps in 3:

1) Select the menu "PLC > Clear" in Micro/WIN Select all three blocks and confirm with "OK".

2) Another method is to restore the default settings of the CPU through the program "wipeout.exe". This program can be found on the STEP7-Micro/WIN installation CD;

3) In addition, an external memory card containing an unencrypted program can also be inserted in the CPU. After the power is turned on, this program is automatically loaded into the CPU and overwrites the original program with a password. Then the CPU is free to access.

39: Can I normally use POU encryption?

The POU is the program organization unit, which includes the main program (OB1), subroutine, and interrupt service program in the S7-200 project file.

The POU can be encrypted separately. The encrypted POU will display a lock mark and cannot open the view program content. The program is downloaded to the CPU and remains encrypted after being uploaded.

The library instructions provided by the programming software Micro/WIN, the subroutines generated by the instruction wizard, and the interrupt program are all encrypted by Siemens. Encryption does not prevent the use of them.

40: Can I encrypt the entire project file?

With Step7 - Micro/WIN V4.0 or higher, users can encrypt the entire Project file so that people who do not know the password cannot open the project.

In the Micro/WIN File menu's Set Password command, enter the project file password up to 16 characters in the pop-up dialog box.

The password can be a combination of letters or numbers, case-sensitive.

41: How to open the project file created by the old version of Micro/Win?

On the genuine STEP7 Micro/WIN software CD, you can find the V2.1 version of the Micro/WIN installation software in the Old Realeses folder. This version of Micro/WIN can open project files created by previous versions. By using it as a bridge, after the old version of the software is saved, it can be opened in the latest version of STEP7 Micro/WIN software.

Note: If it is found that some networks are displayed as red invalid, it may be that the PLC model is too low and the version is too old. In this case, select a high model or a new version of the CPU. For example, change CPU222 to CPU224 in PLC > Type in the command menu.

42: How do you know the size of your program?

After executing PLC > Compile in the command menu in Micro/WIN, you can find the size of the program you programmed, the size of the occupied data block, etc. in the display window (message output window) under Micro/WIN.

43: What should I do if I get a compilation error?

After compilation, if there is something wrong, you will not be able to download programs to the CPU. You can view the error in the window below Micro/WIN. Double-click the error to enter the location of the error in the program. Modify it according to the instructions in the system manual.

44: How do you know the scanning time of your program?

After the program is run once, you can view PLC > Information online in the command menu in Micro/WIN to find the scan time of the program in the CPU.

45: How to find out whether the used program address space is reused?

After compiling the program, you can click on the Cross Reference button in the View navigation bar to see detailed cross-reference information and the use of bytes and bits for the elements used in the program. In cross-reference, you can directly click on the address to enter the address of the program.

46: Why is the function block in the program block turned red during online monitoring?

If you monitor online in the program editor and find a red command function block, it indicates that an error or problem has occurred. You can find the error that caused ENO=0 from the system manual. If it is a "non-fatal" fault, you can check the error type in the menu PLC > Information dialog box.

For NetR/NetW (Network Read/Write), XMT/RCV (Freeport Send/Receive), PLS, etc., instructions related to the PLC operating system or hardware settings turn red at run time, most likely due to instructions Still called in the process of execution, or the communication port was busy.

47: How to use S7-200 high-speed input and output?

The high-speed input and output terminals on the S7-200 CPU have the same wiring as ordinary digital I/O. However, high-speed pulse output must use a DC transistor output type CPU (ie, DC/DC/DC type).

48: Can the NPN/PNP output rotary encoder (and other sensors) be connected to the S7-200 CPU?

Can be. The digital input on the S7-200 CPU and expansion module can be connected to the source or sink sensor output. When connecting, just change the connection of the common terminal accordingly (is the power supply L+ connected to the input common or the power supply M is connected to Public side).

49: Can the S7-200 use a two-wire digital (switch) sensor?

Yes, but the quiescent operating current (leakage current) of the sensor must be less than 1mA. Siemens has related products such as proximity switches (BERO) for PLCs.

50: Does the S7-200 have multiple input and output modules that can be reused?

The digital and analog input/output points of the S7-200 cannot be multiplexed (that is, both as input and output).

51: CPU224 XP high-speed input and output in the end can reach 100K or 200K?

The new product CPU224 XP high speed input supports higher speeds. When used as a single-phase pulse input, it can reach 200KHz; when used as a dual-phase 90° quadrature pulse input, the speed can reach 100KHz.

The CPU224 XP's two high-speed digital output rates can reach 100KHz.

52: The CPU224 XP high-speed input (I0.3/4/5) is a 5VDC signal. Can other input points be connected to the 24VDC signal?

can. Simply connect the common side of the two signal power supplies to the 1M terminal. Both signals must be either sink or source input signals.

53: CPU224 XP high-speed output point Q0.0 and Q0.1 connected to 5V power supply, other points such as Q0.2/3/4 can be connected to 24V voltage?

No. The same voltage level must be connected in groups.

54: There are even analog filters that cannot be filtered?

Because the principle of the analog conversion chip on the CPU 224 XP is different from that of the expansion analog module, no filtering is needed.

55: What is unipolar, bipolar?

Bipolarity means that the signal goes through “zero” during the change, and the unipolarity is zero. Since the analog quantity is converted to a digital quantity as a signed integer, the corresponding value of the bipolar signal will have a negative value. In the S7-200, the unipolar analog input/output signal has a value range of 0 - 32000; the bipolar analog signal has a value range of -32000 - +32000.

56: Can different channels of the same module connect to current and voltage input signals respectively?

Can be wired according to the requirements of current and voltage type signals, respectively. However, the DIP switch setting is valid for all channels of the entire module. In this case, the current and voltage signal specifications must be set to the same DIP switch state. As shown in Table 1 and Table 2 above, the 0 - 5V and 0 - 20mA signals have the same DIP setting status and can be connected to different channels of the same analog module.

57: How should the analog quantity be converted into the desired engineering quantity?

Analog input/output can be converted using the following general conversion formulas:

Ov = [(Osh - Osl)*(Iv - Isl)/(Ish - Isl)] + Osl

among them:

Ov: Conversion result

Iv: Conversion object

Osh: High limit of the conversion result

Osl: Lower Limit of Conversion Results

Ish: The high limit of the conversion object

Isl: The lower limit of the conversion target

59: Why is the analog quantity a very volatile unstable value?

It may be due to the following reasons:

You may use a self-powered or isolated sensor power supply. The two power supplies are not connected to each other. That is, the power supply ground of the analog input module and the signal ground of the sensor are not connected. This will produce a very high common-mode voltage that will vibrate up and down, affecting the analog input value.

Another reason may be that the analog input module wiring is too long or the insulation is not good.

Can be solved by the following method:

1) Connect the negative input of the sensor input to the common M terminal on the module to compensate for this fluctuation. (But take care to ensure this is the only connection between the two power systems.)

The background is:

The analog input module is not isolated inside;

Common mode voltage should not exceed 12V;

The common mode rejection ratio for the 60 Hz interference signal is 40 dB.

2) Use an analog input filter.

60: Why does the SF red light on the EM231 module flash?

There are two reasons why the SF flashes red: The internal software of the module detects that the external thermal resistance is broken or the input is out of range. Since the above detection is common to both input channels, the SF lamp must flicker when only one channel has an external thermal resistance. The solution is to connect a 100 Ohm resistor to the empty channel in the same way as the used channel, or to connect all the leads of the connected thermal resistor to the empty channel.