1. Why should the S7-200 PLC use the PC/PPI interface?
The S7-200 CPU uses RS485, while the COM port of the PC uses RS232. The electrical specifications of the two are not compatible, requiring an intermediate circuit for matching. The PC/PPI is essentially an RS485/RS232 matching cable.
2. What are the advantages of transistor output versus relay output?
Transistors cannot handle AC220V loads and can only drive low-voltage DC. They have poor overload and overvoltage resistance. However, they can output at high frequencies, making them suitable for high-frequency applications, such as pulse control.
Relays can handle both AC220V and DC loads. However, the characteristics of relays prevent them from outputting at high frequencies. Additionally, the lifespan of relay switching is generally around 100,000 cycles. Therefore, in applications requiring frequent switching, transistors are also suitable.
3. What is the communication distance of the communication port on the S7-200 CPU?
The data provided in the “S7-200 System Manual” states that the communication distance is 50m under compliant network conditions. For distances exceeding 50m, a repeater should be added. Adding one repeater can extend the communication network by 50 meters. If a pair of repeaters is added, and there are no S7-200 CPU stations in between (EM277 can be present), the distance between repeaters can reach 1000 meters. Meeting the above requirements ensures very reliable communication.
In practice, some users have achieved communication over distances greater than 50m without adding repeaters. Siemens cannot guarantee that such communication will always be successful.
4. How to set the communication port parameters?
By default, the communication port of the S7-200 CPU is in PPI slave mode, with an address of 2 and a communication rate of 9.6K. To change the address or communication rate of the communication port, it must be set in the communication port tab of the system block, and then the system block must be downloaded to the CPU for the new settings to take effect.
5. What to do if the M area address is insufficient?
Some users habitually use the M area as an intermediate address, but the M area in the S7-200 CPU has a very small address space of only 32 bytes, which is often insufficient. The S7-200 CPU provides a large amount of V area storage space, which is the user data space. The V storage area is relatively large, and its usage is similar to that of the M area, allowing access to V area data by bit, byte, word, or double word. For example: V10.1, VB20, VW100, VD200, etc.
6. What are the methods for long-distance communication with the S7-200?
-
RS-485 network communication: PPI, MPI, and PROFIBUS-DP protocols can communicate over RS-485 networks, and with repeaters, the maximum distance can reach 9600 meters.
-
Fiber optic communication: In addition to anti-interference and high speed, long communication distance is also a significant advantage. The S7-200 products do not directly support fiber optic communication and require an additional fiber optic conversion module.
-
Telephone network: The S7-200 supports telephone network communication through the EM241 audio modem module. The EM241 requires the communication endpoint to be a standard audio telephone line, regardless of the inter-office communication method. Global communication can be achieved through the EM241.
-
Wireless communication: The communication distance of the S7-200 via radio stations depends on factors such as frequency, power, and antenna; the communication distance via GSM networks depends on the coverage of the network service; communication via infrared devices also depends on their specifications.
7. Which communication protocols supported by the S7-200 are public and which are not?
-
PPI protocol: Siemens internal protocol, not public
-
MPI protocol: Siemens internal protocol, not public
-
S7 protocol: Siemens internal protocol, not public
-
PROFIBUS-DP protocol: Standard protocol, public
-
USS protocol: General serial communication protocol for Siemens drive devices, for public details refer to the corresponding drive device manual
-
MODBUS-RTU (slave): Public
8. How to use high-speed inputs and outputs on the S7-200?
The wiring of the high-speed input and output terminals on the S7-200 CPU is the same as that of ordinary digital I/O. However, high-speed pulse outputs must use a DC transistor output type CPU (i.e., DC/DC/DC type).
9. Can NPN/PNP output rotary encoders (and other sensors) be connected to the S7-200 CPU?
Yes, both can be connected. The digital inputs on the S7-200 CPU and expansion modules can connect to source-type or sink-type sensor outputs, and the connection can be made by appropriately changing the common terminal connections.
10. How to mix NPN and PNP sensors into the S7-200 PLC?
It is well known that Japanese PLCs such as Mitsubishi and OMRON generally use NPN sensors for signal input, while European PLCs typically use PNP sensors. In the case of S7-200/300, if the provided sensors include both PNP and NPN types, how can this be resolved?
Method 1: Use an intermediate relay to connect NPN sensors.
Method 2: When designing, generally connect the input terminals of the 200 PLC to 24V-, while the 200 PLC can also accept – signal inputs. Connect 1M to 24V, and I0.0-0.7 to NPN sensors, while connecting 2M to 24V- and PNP sensors to I1.0-1.7, thus achieving the purpose of mixing NPN and PNP sensors into the PLC. The reason is simple: the 200 PLC supports two types of signal inputs, and internally uses bidirectional diodes with optical isolation for signal transmission.
11. How does a high-speed counter occupy output points?
The high-speed counter occupies digital input points on the CPU according to its defined working mode. Each counter occupies a fixed number of input points based on its working mode. Input points not used in a certain mode can still be used as ordinary input points; input points occupied by the counter (such as external reset) can still be accessed in the user program.
12. Why does the high-speed counter not work properly?
In the program, the initial scan memory bit SM0.1 must be used to call the HDEF instruction, and it can only be called once. If SM0.0 is used to call or if the HDEF instruction is executed a second time, it will cause a runtime error and cannot change the settings made during the first execution of the HDEF instruction for the counter.
13. How to address the high-speed counter? Why can’t the current count value be read from SMDx?
High-speed counters can be addressed directly using HC0, HC1, HC2, HC3, HC4, HC5 to read the current value, or the above addresses can be entered in the status table to directly monitor the current value of the high-speed counter. SMDx does not store the current value. The count value of the high-speed counter is a 32-bit signed integer.
14. How to reset the high-speed counter to 0?
Select a high-speed counter with an external reset mode; when the external reset input signal is valid, the high-speed counter resets to 0. It can also be reset using an internal program by setting the high-speed counter to an updatable initial value and setting the initial value to 0. After executing the HSC instruction, the high-speed counter will reset to 0.
15. Why do initial and preset values not work or have unexpected effects when assigned to the high-speed counter?
The high-speed counter can change settings such as initial and preset values during initialization or operation. The operation steps should be:
-
Set the update options for the control byte. For the settings that need to be updated, set the corresponding control bits in the control byte to “1”; for settings that do not need to be changed, the corresponding control bits should not be set.
-
Then send the desired values to the initial value and preset value control registers.
-
Execute the HSC instruction.
Mitsubishi FX Series PLC
1. What are the differences between FX3G and FX3GA?
1. FX3GA: The input/output terminal block is non-removable; FX3G is removable, so when replacing the PLC, there is no need to disconnect the wiring;
2. FX3GA: Cannot be equipped with optional batteries; FX3G can be equipped with batteries;
3. FX3GA: Can only expand one BD communication board (single-channel expansion); FX3G with 40 points or more can expand 2 BD boards (dual-channel expansion);
4. FX3GA: Assembled domestically; FX3G is completely produced abroad.
2. What adjustments and changes are needed when replacing FX2N with FX3U and FX3UC?
1. The dimensions of the FX3U(C) series correspond to the FX2N(C) series, so there is no need to change the cabinet installation;
2. The input/output terminal block size and position of the FX3U(C) series are the same, so there is no need to disconnect the wiring when replacing the PLC; the old terminal block can be directly transferred to the new machine;
3. The wiring of FX3UC and FX2NC is completely the same; FX3U will have an additional input signal type selection S/S terminal, which needs to be shorted to 24V, while the corresponding position of FX2N was vacant.
3. What download cables are available for the FX series PLC, and what are their differences?
The FX series download cables include FX-USB-AW (original), USB-SC09-FX, USB-SC09, SC09.
1. FX-USB-AW is the original FX dedicated download cable from Mitsubishi, with a USB interface on the computer side, reliable and convenient to use;
2. USB-SC09-FX is a domestic imitation of the Mitsubishi FX-USB-AW download cable, with a USB interface on the computer side, convenient to use;
3. USB-SC09 is a domestic download cable that can be used for FX series PLCs and A series PLCs, with a USB interface on the computer side, convenient to use;
4. SC09 is mainly for older computers (with built-in RS232C 9-pin interface), with an RS232 interface on the computer side. Now, to use it on modern computers, a USB to RS232 adapter is needed, such as USB-RS232 2.0.
4. Do the original modules need to be replaced when replacing FX2N PLC with FX3U?
1. When replacing FX2N PLC with FX3U, the original function expansion boards (communication BD boards and special adapters like FX2N-485BD, FX2NC-232ADP) need to be replaced with corresponding FX3U series function expansion boards;
2. Expansion devices (input/output modules, special function modules like FX2N-16EX, FX2N-2AD) do not need to be replaced and can be used directly.
5. Is it necessary to use an FX2N-CNV-BC conversion connector to connect the FX0N-65EC extension cable?
When connecting FX0N-65EC to FX2N-32ER/ET, FX2N-48ER/ET, it is not necessary to add FX2N-CNV-BC.
6. What is the difference between the suffix ES/UL and -001 for FX2N series PLC models?
1. The suffix ES/UL indicates the European version, while -001 indicates the mainland China version.
2. The ES/UL series input method can be selected through S/S terminals, allowing for source-type and sink-type input methods, while the -001 series input method is fixed as sink-type input.
7. Is it necessary to add an FX2N-CNV-BC conversion connector to connect the FX0N-65EC?
When connecting FX0N-65EC to FX2N-32ER/T or FX2N-48ER/T, it is not necessary to add FX2N-CNV-BC; other modules do require it.
8. How many axes can the built-in high-speed pulse output points of FX1S, FX1N, FX2N, FX3G, FX3GA, FX3U(C) control?
1. FX1S and FX1N can control 2 independent axes, with a maximum output of 100KHZ pulse trains.
2. FX1NC can control 2 independent axes, with a maximum output of 10KHZ pulse trains.
3. FX2N can control 2 independent axes, with a maximum output of 20KHZ pulse trains.
4. FX3G and FX3GA with 14/24 points can control 2 independent axes, with 40/60 points having a maximum output of 100KHZ pulse trains.
5. FX3U and FX3UC can control 3 independent axes, with a maximum output of 100KHZ pulse trains.
9. Can the FX1N PLC expand and connect to FX2N input/output modules, analog modules, positioning modules, etc.?
The FX1N PLC can fully expand and connect to FX2N expansion modules, such as FX2N-16EX, FX2N-16EYR, FX2N-4AD, FX2N-10GM, FX2N-20GM, etc.
10. What to do if the power LED on the FX series PLC goes out or flashes during operation?
Disconnect the wiring on the [24] (working power) terminal of the PLC to confirm whether it returns to normal.
1. If it returns to normal, it may be due to a short circuit or excessive load current causing the working power capacity to overload, triggering the protection function.
2. If it does not return to normal, please contact a professional technician for repair.
11. What is the difference between FX3U-ENET-ADP and FX3U-ENET-L, and can they replace each other?
FX3U-ENET-L is an Ethernet module, while FX3U-ENET-ADP is an Ethernet port adapter; the -L has powerful functions and can replace ADP; whether the reverse can replace it depends on whether the functions used can be met.
1. Both ENET-ADP and ENET-L have MELSOFT connection functions, which allow connection to human-machine interfaces such as Mitsubishi and Wecon touch screens via Ethernet.
2. Both ENET-ADP and ENET-L have MC protocol (Mitsubishi PLC dedicated protocol), which allows upper-level industrial control computers to read, write, and control the PLC using the MC protocol.
3. The ENET-L module has a large buffer and supports caching for sending and receiving (1024 words/time), allowing it to communicate as a master station with third-party devices such as instruments, while ENET-ADP is just a communication expansion port without this function.
12. Can FX3U-1PG replace FX-1PG-E?
1. FX3U-1PG is an upgraded version of FX2N-1PG/FX-1PG-E; performance has improved with pulse output up to 200KHZ, and their programs are compatible.
2. FX3U-1PG can only be used on FX3U PLC main units; after replacement, ensure that the main unit is FX3U PLC.
13. How to communicate between Mitsubishi FX3G series PLC and barcode scanners? How to read barcodes in Mitsubishi 3G PLC?
Use RS instructions; to read the barcode from the scanner, you must know its communication protocol, whether it is proprietary or MODBUS protocol, and then know the address of the barcode data storage area and the data type and size, so that you can use RS instructions to read the data from the barcode storage area address. If it is two words, just display the contents of those two words.
14. I am preparing to try to make a control system to control a stepper motor, four cylinders, and four proximity switch inputs. Which PLC model is cost-effective?
For such a simple system, any model will do; FX2N, FX1S, or FX3U can be selected, as long as it has transistor outputs.
15. How to control a servo motor with a PLC?
Calculate the distance per revolution based on the encoder resolution, and then control it with pulses.
16. What are the parameters corresponding to the 4-20mA current output of the 4AD module of the Mitsubishi FX3U series PLC?
800-4000.
17. Is it necessary to use a servo with the PLC positioning module?
It must be used with a servo, as positioning data is output to the servo amplifier based on parameters.
18. Which is better, the Mitsubishi FX3GA series PLC or the Mitsubishi FX3U series PLC?
Choose based on specific applications; the software is the same.
19. What are the programming differences among these Mitsubishi PLC series?
There is basically no difference; most instructions between FX2NC and FX3U are compatible.
