1 : How can I avoid the "communication failure" message when using CPU315F and ET200S?
Using the CPUS7315F, ET200S, and fail-safe DI/DO modules, you will invoke the fail-safe procedure of OB35. Furthermore, you have accepted the default settings for all monitoring times and are willing to receive "communication failure" messages. OB35 is set to 100 milliseconds by default. You have set the F monitoring time of the FI/O module to 100 milliseconds, therefore the I/O module should be addressed at least once every 100 milliseconds. However, since OB35 is only invoked once every 100 milliseconds, a communication failure will occur. To ensure that the OB35 scan interval and the F monitoring time differ, ensure that the F monitoring time is greater than the OB35 scan interval.
This issue has been present in the S7 distributed security system up to versions V5.2SP1 and 6ES7138-4FA00-0AB0, 6ES7138-4FB00-0AB0, and 6ES7138-4CF00-0AB0. In the new module, the monitoring time for F is set to 150 milliseconds.
2: When the DP slave is unavailable, what is the monitoring time of the S7-300 CPU on PROFIBUS?
When operating a PROFIBUS network using a DP slave on the CPU's PROFIBUS interface, it is desirable to check whether the expected configuration matches the actual configuration during startup. Two different times are provided on the Startup tab of the CPU Properties dialog box.
3: How to determine if there is a problem with the power supply or buffer, such as a battery failure?
If an event is triggered by a power supply (S7-400 only) or buffer error, the CPU operating system accesses OB81. After the error is corrected, OB81 is accessed again. In the event of a battery failure, if the BATT.INDIC switch in battery detection is active, the S7-400 only accesses OB81. If OB81 is not configured, the CPU will not enter the STOP operating state. If OB81 is unavailable, the CPU continues to run even when a power supply error occurs.
4: What issues should be considered when allocating addresses for I/O modules (centralized or distributed) on the S7 CPU?
Please note that data regions (such as a double word) cannot be configured on the boundaries of a process image because only the area below the boundary can be read into the process image within that data block, making it impossible to access data from the process image. Therefore, these configuration rules do not support this situation: for example, configuring an input double word at address 254 of a 256-byte input process image. If such addressing is absolutely necessary, the size of the process image must be adjusted accordingly (in the CPU's Properties).
5: How is basic global data communication performed in the S7 CPU? What precautions should be taken during communication?
Global data communication (GD) is used to exchange small amounts of data. GD can be both input and output.
mark
Data in data blocks
Timer and counter functions
Data exchange refers to the exchange of data in the form of data packets between CPUs connected to a one-way or two-way GD ring. GD rings are identified by GD ring numbers.
One-way connection: A single CPU can send GD data packets to multiple CPUs.
Bidirectional connection: A connection between two CPUs: Each CPU can send and receive a GD data packet.
It must be ensured that the receiving CPU has acknowledged the receipt of global data. If data exchange is to be performed via appropriate communication blocks (SFB, FB, or FC), a connection must be established between the communication blocks. Defining a connection greatly simplifies the design of communication blocks. This definition is valid for all called communication blocks and does not need to be redefined each time.
6: Can the S7-400 memory card be used with the CPU318-2DP?
In normal operation, only the "short" memory cards with order numbers 6ES7951-1K... (FlashEPROM) and 6ES7951-1A... (RAM) can be used.
7: Even though the LED is on, why can't the CPU31xC read complete input from the default addresses 124 and 125?
For the following CPU models, please check if the 24V voltage is connected to pin 1. The LED is controlled by the input current. The 24V voltage on pin 1 requires further processing.
313C(6ES7313-5BE0.-0AB0),313C-2DP(6ES7313-6CE0.-0AB0),313C-2PTP(6ES7313 -6BE0.-0AB0),314C-2DP(6ES7314-6CF0.-0AB0),314C-2PTP(6ES7314-6BF0.-0AB0)
8: When configuring the PN interface of CPU31x-2PN/DP, how should we handle occasional communication errors on the PROFINET interface?
Please ensure that all components (converters) in the Ethernet (PROFINET) network support 100 Mbit/s full-duplex basic operation. Avoid central distributors that disrupt the network, as these devices can only operate in half-duplex mode.
9: What does the "clock" correction factor mean in the hardware configuration editor?
In the hardware configuration, you can specify a correction factor in the "Clock" field via CPU > Properties > Diagnostics/Clock. This correction factor only affects the CPU's hardware clock. Time interrupts originate from the system clock and are unrelated to the hardware clock settings.
10: How to implement bidirectional data transmission between master and slave stations using PROFIBUSDP function blocks?
The master PLC can exchange data with the slave station by calling SFC14 "DPRD_DAT" and SFC15 "DPWR_DAT", while the slave station can exchange data by calling FC1 "DP_SEND" and FC2 "DP_RECV".
11: What identification data can be read from the S7 CPU?
The following identification data can be read using SFC51 "RDSYSST":
The order number and CPU version number can be read. For this, use SFC51 and SSLID0111 and the following index:
1 = Module identifier
6 = Basic Hardware Identifier
7 = Basic Firmware Identifier
12: On an S7-300 containing a CPU317-2PN/DP, how can I program it to load communication function blocks FB14("GET") and FB15("PUT") for data exchange?
To exchange data between two S7-300 workstations using a CPU317-2PN/DP via an S7 connection configured with NetPro, communication function blocks must be invoked during S7 communication. Module FB14 ("GET") is used to retrieve data from the remote CPU, and module FB15 ("PUT") is used to write data to the remote CPU. These function blocks are included in the standard library of STEP7 V5.3.
FB14 and FB15 are asynchronous communication functions. These modules may run across multiple OB1 loops. FB14 or FB15 is activated by inputting the REQ parameter. DONE, NDR, or ERROR indicate the job has ended. PUT and GET can communicate simultaneously via the connection.
Note: Communication blocks from the SIMATIC_NET_CP library cannot be used with CPU317-2PN/DP.
13: What should be noted when processing jobs synchronously on compact CPU313C-2PtP and CPU314-2PtP?
In user programs, it is not possible to program both SEND and FETCH jobs simultaneously.
Right now:
The FETCH job (SFB64) cannot be called unless the SEND job (SFB63) has been completely terminated (DONE or ERROR).
(Even when REQ=0).
The SEND job (SFB63) cannot be called unless the FETCH job (SFB64) has completely terminated (DONE or ERROR).
(Even when REQ=0).
While processing an active job (SEND job, SFB63 or FETCH job, SFB64), a passive job can also be processed simultaneously.
(SERVE assignment, SFB65).
14: Can the MICR. master420 to 440 be run together with the CPU317T as a configuration axis (external position detection)?
Yes, but the requirements for configured axes differ greatly in terms of power and precision. For high-demand applications, servo drives such as SIMODRIVE611U, MASTERDRIVESMC, or SINAMICSS must operate in conjunction with the CPU317T. For lower-demand applications, the MICROMASTER series can also meet the power and precision requirements.
15: How to configure direct data exchange (inter-node communication) between two CPU modules that have been configured as DP slaves?
Two CPU stations are configured as DP slave stations and operated by the same DP master station. Communication between them can be achieved by configuring the exchange mode to DX and directly exchanging data.
16: How to communicate using SFC65, SFC66, SFC67 and SFC68?
For unidirectional basic communication, system function SFC67 (X_GET) is used to read data from a passive station, and system function SFC68 (X_PUT) is used to write data to a passive station (server). These blocks are only invoked in the active station. For bidirectional basic communication, system function SFC65 (X_SEND) is invoked in the station to send data to another active station. In the active receiving station, which is also active, the data is recorded via system function SFC66 (X_RCV).
In both types of basic communication, each block call can handle a maximum of 76 bytes of user data. For the S7-300 CPU, data transmission consistency is 8 bytes, while for the S7-400 CPU it is the full length. If connecting to an S7-200, it must be considered that the S7-200 can only be used as a passive station.
17: What is free allocation of I/O addresses?
The ability to freely assign addresses means you can freely assign an address to each module (SM/FM/CP). Address assignment is done in STEP7. First, define the starting address, and then use it as the base for all other addresses of that module.
The advantages of freely allocating addresses are: because there are no address gaps between modules, the available address space can be used optimally. When creating standard software, the configuration of the S7-300 involved can be disregarded during the address allocation process.
18: What can a diagnostic buffer do?
More rapid identification of fault sources improves system availability. Evaluate the last event prior to the stop and identify the cause of the stop.
The diagnostic buffer is a circular buffer with a single diagnostic entry displayed in the sequence of events; the first entry shows the most recently occurred event. If the buffer is full, the oldest event is overwritten by a new entry. Depending on the CPU, the size of the diagnostic buffer may be fixed or can be configured via parameters in HWConfig.
19: What entries are included in the diagnostic buffer?
1) Fault events
2) Changes in operating modes and other operational events that are important to users.
3) User-defined diagnostic events (using SFC52WR_USMSG)
In STOP mode, the number of events stored in the diagnostic buffer should be minimized so that the user can easily find the cause of the STOP within the buffer. Therefore, entries are only stored in the diagnostic buffer when an event requires a response from the user (such as scheduling a system memory reset or the battery needing to be charged) or when important information must be registered (such as a firmware update or station failure).
20: How do I determine the size of the MMC to fully store a STEP7 project?
To select the appropriate MMC for a project, it's necessary to understand the overall project size and the size of the chunks to be loaded. The project size can be determined using the following method:
1) First, archive the STEP7 project. Then, open the archived project in Windows Explorer and determine its size (select the project and right-click). This will tell you the size of the archive file.
2) Load the block into the CPU. You still need to select "PLC > Module Information > Memory". Here, under "Load memory RAM + EPROM", you can see the size of the allocated memory.
3) This value must be added to the already determined size of the archived project. This will give you the total memory required to store the entire project on an MMC.
21: Which settings will be retained after a full CPU reset?
When the CPU is reset, the memory is not completely erased. The entire main memory is completely erased, but the data in the loaded memory, as well as the data stored on the Flash-EPROM memory card (MC) or Micro Memory Card (MMC), are all retained. In addition to the loaded memory, timers (except for the CPU312IFM) and diagnostic buffers are also retained. CPUs with an MPI interface or a combined MPI/DP interface only retain the current address and baud rate used by the interface before a full reset. On the other hand, the other PROFIBUS address is also completely erased and can no longer be accessed.
Important: After resetting PG/PC, communication with the CPU can only be established through the MPI or MPI/DP interface.
22: Why can't the CPU be accessed online via MPI?
If you have already changed the MPI parameters on the CPU, please check the hardware configuration. You can compare these values with the parameters under "SetPG/PCinterface" to see if there are any inconsistencies.
Alternatively, you can do this: Open a new project and create a new hardware configuration. In the CPU's MPI interface properties, set the values for address and transfer speed. Write an "empty" entry to the memory card. Insert the memory card into the CPU and then turn the CPU voltage back on, transferring the settings from the memory card to the CPU. Now the current settings for the MPI interface have been transferred, and as such, a connection can be established as long as the interface is functioning correctly. This method works for all S7 CPUs with a memory card interface.
23: What is the purpose of an error OB?
If a described error occurs (see File 1), the corresponding OB will be invoked and processed. If the OB is not loaded, the CPU will enter a STOP state (exceptions: OB70, 72, 73, and 81).
The S7 CPU can identify two types of errors:
1) Synchronization errors: These errors are triggered during the processing of a specific operation and can be attributed to a specific part of the user program.
2) Asynchronous errors: These errors cannot be directly attributed to a running program. These errors include priority-based errors, errors in automated systems (faulty modules), or redundant errors.
24: Which "fault OBs" should be programmed in the DP slave station or CPU315-2DP master station?
When configuring a CPU315-2DP station as a slave, the following operations block (OB) must be programmed in the STEP7 program to evaluate error messages of distributed I/O types:
OB82 diagnostic interrupt; OB86 subrack fault; OB122 I/O access error.
1) Diagnostic OB82: If a module that supports diagnostics and has already released its diagnostic interrupt detects an error, it sends a diagnostic interrupt request to the CPU for both incoming and outgoing events. The operating system then calls OB82. OB82's own local variables contain the logical base address of the faulty module and 4 bytes of diagnostic data. If you haven't programmed OB82, the CPU enters "stop" mode. You can block or delay the diagnostic interrupt OB and release it again via SFC39-42.
2) Subrack Fault OB86: If a fault is detected in a DP master system or a distributed I/O station (for both incoming and outgoing events), the CPU's operating system calls OB86. If OB86 is not programmed but such an error occurs, the CPU enters "stop" mode. You can block or delay OB86 and then release it via SFC39-42.
3) I/O Access Error OB122: When an error occurs while accessing data in a module, the CPU's operating system calls OB122. For example, if the CPU detects a read error while accessing data in a single module, the operating system calls OB122. OB122 operates with the same priority class as interrupt blocks. If OB122 is not programmed, the CPU switches from "run" mode to "stop" mode.
25: Why are reserved sections sometimes overwritten?
In the STEP7 hardware configuration, several operand areas can be defined as "reserved areas." This allows the contents of these areas to be retained even after a power outage, without a backup battery. If a block is defined as a "reserved block," but it does not exist in the CPU or is only temporarily installed, some of the contents of these areas will be overwritten. After power is turned on/off, the remaining contents will be found in the relevant areas.
26: Why can't the contents of the flash memory card be loaded into the S7300 CPU?
Your project is on a flash memory card. You're trying to load it onto an S7300. However, after loading, the CPU's RAM is still empty. This problem occurs because your program contains an unprocessable, "incorrect" organization block (for example, OB86 lacks a DP interface). Even after resetting and restarting the CPU, the RAM remains empty. The diagnostic buffer will provide some information about this "unloadable" block.
27: Diagnostic address when CPU315-2DP is used as both slave and master stations.
When configuring a CPU315-2DP station, you use the S7 tool "H/WCONFIG" to assign diagnostic addresses. If a fault occurs, these diagnostic addresses are added to the diagnostic OB variable "OB82_MDL_ADDR". You can analyze this variable in OB82 to identify the faulty station and take appropriate action.
Below is an example of how diagnostic addresses are allocated:
Step 1: Configure the slave station via CPU315-2DP and assign it a diagnostic address, such as 422.
Step 2: Configure the master station via CPU315-2DP
Step 3: Link the configured slave station to the master station and assign it a diagnostic address, such as 1022.
28: What settings need to be made to the DP slave interface of the S7-300 CPU in order to use it for routing?
If you are using a CPU as an I-Slave, and that CPU also functions as an S7 router, please note the following:
The DP interface of the slave used for routing must be set to active. This can be done in HWConfig: in the DP interface's properties dialog box, the option "Commissioning/Testoperation" or "Programming,status/modify..." must be activated. Notes regarding these settings can be found in the table below.
For S7 routing connections, there are four available connection resources—unrelated to any other connection resources. No PG/OP connection resources or S7 basic communication are used.
If a connection to a communication partner located on its rack must be established via the DP interface (as in the CP343-1), a routed connection must also be used. However, for connections to a communication partner located on its rack via the MPI interface, routed connection resources are not used because the partner can be reached directly in this case. Note: This does not apply to the CPU318.
29: Why is there no return value when using the internal runtime schedule of the S7-300 CPU?
When parameterizing system function blocks SFC2, SFC3, and SFC4 from CPU312IFM to 316-2DP, if an identifier greater than "B#16#0" is specified for a runtime schedule, an error will occur and the required function will be unavailable. In this case, the identifier "8080h" will be output at the "RETVAL" output of the block.
Note: Only one timer is available for these CPUs. Therefore, you should only use the identifier "B#16#0". The system function SFC2 "SET_RTM" must not be called within a cycle block (OB1, OB35); it should be called during the restart of OB (OB100). You can also start the block using an external trigger. Otherwise, the block will constantly reset and run the timer, never completing the count.
30: How are variables stored in temporary local data?
The L stack always begins at address "0". Within the L stack, the same number of bytes are reserved for each data block to store its static or local data.
When a block terminates, its space is released. The pointer always points to the first byte of the currently open block.
31: After the CPU undergoes a complete reset, is the runtime counter also reset?
When using the S7-300, there is a difference between CPUs with a hardware clock (the built-in "real-time clock") and those with a software clock. For CPUs with a software clock and no backup battery, the runtime counter's last value is deleted after a complete CPU reset. However, for CPUs with a hardware clock and a backup battery, the runtime counter's last value is retained after a complete CPU reset. Similarly, the runtime counter of the CPU318 and all S7-400 CPUs is retained after a complete CPU reset.
32: How do I configure an S7 CPU that is not in the same project as a DP slave of my S7 DP master module?
By default, only one S7 CPU can be configured as a slave in STEP 7 if it is within the same project. This slave then appears as "CPU31x-2DP" in the hardware directory under "PROFIBUS-DP > Configured Stations". This method allows you to set up a link between a DP master and a DP slave.
There is also an option to configure an S7 CPU that is not in the same project as the master station as a slave station. The procedure is as follows:
Configure the DP slave station as usual.
Download the GSD file for the S7-300 CPU you want to use as a slave from the internet. The file is located under "PROFIBUS GSD Files/SIMATIC" at the customer support website.
Open SIMATICManager and Hardware Configuration.
Open "Options; Install new GSD..." and insert the downloaded GSD file into the hardware directory. (Note: No window needs to be opened in HWConfig during this process.)
Update the hardware catalog using "Options; Update Catalog".
You can now configure your DP master. The S7-300 CPU, acting as a slave, will be found under "PROFIBUS-DP > More Field Devices > SPS".
Note: If you are manually connecting the DP slave, you must ensure that the bus parameters, the PROFIBUS address of the DP slave, and its I/O configuration are the same in both items.
33: Is the impact of a power outage in the absence of a backup battery the same as a complete reset?
No, they are different. When the CPU is completely reset, its hardware configuration information (except for the MPI address) is deleted, the program is deleted, and the residual magnetron memory is also cleared.
When power is turned off without a backup battery and memory card, hardware configuration information (except for MPI addresses) and programs are deleted. However, the residual magnetron (RM) is unaffected. If the program is reloaded under these conditions, it will operate using the old values from the RRM. These values, for example, typically come from the first 8 counters. Ignoring this can lead to a dangerous system state.
Recommendation: Always perform a complete reset after a power outage if there is no spare battery or memory card available.
34: Can a 2-wire sensor be connected to the analog input of a compact CPU?
Both 2-wire and 4-wire sensors can be connected to the analog inputs of the CPU300C. When using a 2-wire sensor, set "I=Current" to the measurement type in the hardware configuration, just like the setting for a 4-wire sensor.
Important Notes: Please note that the compact CPU only supports active sensors (4-wire sensors). If using a passive sensor (2-wire sensor), an external power supply is required.
Warning: Please note the maximum permissible input current. The 2-wire sensor may exceed the maximum permissible current in the event of a short circuit. The maximum permissible current specified in the technical datasheet is 50mA (destructive limit). For situations such as (e.g., adding a current limit to the 2-wire sensor or connecting a PTC thermistor in series with the sensor), ensure adequate protection is provided.
35: Can the SM322-1HH01 also work when the load voltage is AC 24V?
Yes, you can also use the SM322-1HH01 with a load voltage of AC 24V.
36: What is the minimum load voltage and current required to ensure that the SM322-1HF01 is turned on?
The SM322-1HF01 relay module requires 17V and 8mA to ensure proper opening and closing. This is better than the values (10V and 5mA) specified in the manual for contact life. The manual's values should be considered the minimum requirements.
37: Which 24V digital input modules (6ES7321-xBxxx-...) need to be connected to a power supply?
Power connector connection for the 24V digital input module (L+/M).
38: Can the SM321 module (DI16x24V) also be used in the ET200M?
The SM321 module (MLFB6ES7321-7BH00-0AB0) can also be used in the ET200M. The CPU31x-2DP can act as a DP master, or the communication processor CPCP342-5 can act as a DP master. Similarly, this module can be connected to an S7-400 CPU via the ET200M and the S7-400 communication processor CP443-5.
39: What address does the SM323 digital card occupy?
The SM323 module comes in two types: 16-bit (6ES7323-1BL00-0AA0) and 8-bit (6ES7323-1BH00-0AA0). For the 16-bit type module, inputs and outputs occupy two addresses, "X" and "X+1". If the base address of the SM323 is 4 (i.e., X=4; slot 5), then the inputs are assigned to addresses 4 and 5, and the outputs are also assigned to addresses 4 and 5. In the module's wiring diagram, the input byte "X" is located at the top left, and the output byte "X" is located at the top right.
For 8-bit modules, inputs and outputs each occupy one byte, and they share the same byte address. If fixed slot addressing is used, and the SM323 is inserted into slot 4, then the input addresses are I4.0 to I4.7, and the output addresses are Q4.0 to Q4.7.
40: Can the SM321-1CH20 be used to replace the SM321-1CH80 without changing the hardware configuration?
The SM321-1CH20 and SM321-1CH80 modules have the same technical specifications. The only difference is that the SM321-1CH80 can be used in a wider range of environmental conditions. Therefore, you do not need to change the hardware configuration.
41: What should be noted when performing direct I/O access?
It's important to note that in an S7-300 configuration, performing cross-module I/O direct read access (using this command to read several bytes at a time) will result in incorrect values. You can check the specific address in the hardware settings.
42: Does the SM321 module need to be connected to DC24V?
No, it's not necessary. If it's an SM321 module with MLFB 6ES7321-1BH02-0AA0, then there's no need to connect to DC24V.
43: How do I plan the SM374 analog module in the STEP7 hardware configuration? How do I find this module in the hardware catalog?
The SM374 analog module can be used in three modes: as a 16-channel digital input module, as a 16-channel digital output module, and as a mixed digital input/output module with 8 inputs and 8 outputs.
Now configure the SM374 according to the modules you need to simulate, that is;
If you are using the SM374 as a 16-channel input module, then the recommended configuration for a 16-channel input module is: SM321: 6ES7321-1BH01-0AA0.
If you are using the SM374 as a 16-channel output module, then the recommended configuration for a 16-channel output module is: SM322: 6ES7322-1BH01-0AA0.
If you use the SM374 as a mixed input/output module, configure a mixed input/output module (8 inputs, 8 outputs) - recommended: SM323:6ES7323-1BH01-0AA0.
44: When measuring current, if a sensor short circuit occurs, will the analog input I+ of module 6ES7331-1KF0.-0AB0 be damaged?
When measuring current, in the event of a sensor short circuit, the analog input I+ of module 6ES7331-1KF0.-0AB0 will not be damaged. This module has built-in overcurrent protection. Each 50-ohm resistor in the module has a PTC element preceding it to prevent damage to the module's input path.
Please note that the maximum allowable long-term input voltage is 12V, and the short-term (maximum 1 second) value is 30V.
45: If the CPU is disconnected, will the 2-wire measurement transmitter continue to be powered?
If the transmitter module is inserted in position "D" and the module is powered by an external voltage on pins 1 and 20, the 2-wire measurement transmitter continues to be powered. Even if the CPU is disconnected, its supply current remains unchanged.
46: When measuring temperature (Fahrenheit) using the S7-300 analog input module, can the absolute error limits listed in the module's documentation be used?
The specified error limits cannot be used directly. Both basic and operational errors are expressed in absolute and Celsius temperatures. They must be multiplied by a factor of 1.8 to convert them to Fahrenheit.
Example: S7-300AI8xRTD: The specified temperature input operating error is +/- 1.0 degrees Celsius. When measured in Fahrenheit, the maximum acceptable error is +/- 1.8 degrees Fahrenheit.
47: Why can't a commercial digital multimeter read the constant current used to read the impedance on the analog input block?
Almost all S5/S7 analog input devices still operate in a complex way: all channels are sequentially plugged into a single A/D converter. This principle also applies to the constant current required to read impedance. Therefore, the current flowing through the resistor to be read is only used for short-term readings. For the SM331-7KF02-0AB0, which has a selected interface rejection "50Hz" and 8 parameterized channels, this means that the current will flow approximately every 180ms, with 20ms of impedance available for reading each time.
48: Why does the voltage output of the S7-300 analog output group exceed the tolerance? What are the uses of terminals S+ and S-?
The following description applies to all SM332 analog output modules:
When using the analog output module SM332, attention must be paid to the assignment of the return inputs S+ and S-. They serve to compensate for performance impedance. When the two contacts of the actuator are connected with separate wires with S+ and S-, the analog output adjusts the output voltage so that the actual voltage present on the actuator is the desired voltage.
To obtain compensation, the actuator must be connected with four wires. This means that for the first channel, the following is required:
The output voltage is connected to the actuator via pins 3 and 6.
Assign pins 4 and 5 to the actuator.
If you do not want compensation, simply bridge pins 3-4 and pins 5-6 on the front switch.
Note: Because the sensor terminals (S+ and S-) are open, the output voltage is regulated to a maximum of 140mV (for 10V). For this configuration, it is impossible to maintain a 0.5% voltage output error limit.
49: How do I connect a potentiometer to 6ES7331-1KF0-0AB0?
The potentiometer's sampling terminal and first terminal are connected to M+, its last terminal is connected to M-, and S- and M- are connected together.
Note: The maximum allowable resistance is 6K. If the potentiometer supports a direct output of a variable voltage, then the first terminal of the potentiometer should be connected to V+ and the M terminal should be connected to M-.
50: How do I connect a PT100 temperature sensor to an analog input module SM331?
The resistance of a PT100 resistance thermometer changes with temperature. If a constant current flows through this thermometer, the voltage drop across it changes with temperature. A constant current is applied across contacts Ic+ and Ic-. The analog module SM331 measures the change in current at M+ and M-. The temperature can be determined by measuring the voltage.
There are three types of connections from the PT100 to the analog input group: a 4-wire connection provides the most accurate measurements.
*Notice:
1) The formula used for the 3-wire connection only shows the actual measurement process of the analog input module SM331 (MLFB number 6ES7331-7Kxxx-0AB0)b".
2) In the S7-300 series, there are some analog inputs that have been measured multiple times. They specify the line resistance of the common return line and perform mathematical compensation. The accuracy obtained is almost comparable to that of a 4-wire connection. An example of such a module is the SM331 (MLFB No. 6ES7331-7PF00-0AB0).
3) The given formulas still apply to the main physical relationships, but do not include an effective measurement process for determining the resistance of PT100.
