PLC HMI Motion controller Drive system
EM231 measurement is unstable

Problem: EM231 measurement is unstable



 If the environment clean ground on the ground, if the environment is poor ground do not ground, do not know the environment of the ground conditions, can choose not to ground.

How to make RS232 cable

Question: How to make a self-made RS232 cable


I have no company programming cable, and the use of our products for RS232 communication, you can make their own RS232 cable.

Desktop comes with nine pin 232 serial port, and notebook computers can use USB to RS232 to get 232 serial port. Our CPU on the RS232 communication pin definition and computer lead-out RS232 definition is not the same, need to be converted. The specific conversion is: 2 (PC) -9 (CPU), 3 (PC) -2 (CPU), 5 (PC) -5 (CPU).

Common problems with temperature measurement modules

Q: Does the EM231 TC need to compensate for the wire?

A: EM231 TC can be set to cold-end compensation, but still need to compensate the wire for thermocouple free end compensation.

Q: Why does the EM light of the EM231 RTD and EM231 TC always blink?

A: If disconnection detection is selected, it may be broken. EM231 RTD unused channel connected to 100 ohm resistance, and for the EM231 TC will need to short the unused channel.

Q: What is positive calibration, negative calibration?

A: The positive calibration value is 3276.7 degrees (Fahrenheit or Celsius), the negative calibration value is -3276.8 degrees. If a break is detected and the input is out of range, the value of the corresponding channel is automatically set to the above calibration value.

Q: The temperature is normal when the boot, but after running for some time, found that the measured temperature is higher than the actual temperature. How is this going?

A: Check if the thermocouple module is installed where the ambient temperature is not uniform. Such as contactors and other heating devices above. When the contactor is hot and the hot air rises, the temperature of the thermocouple module is not uniform, and the cold junction temperature compensation of the EM231 thermocouple module is compensated by the local temperature. This will cause the cold junction temperature compensation of the EM231 thermocouple module to be incorrect, Inaccurate measurements.

Q: What is the reason why the thermocouple module measures the difference between the temperature and the local thermometer?

A: check in the following order:

Check that the thermocouple is consistent with the installation location of the field thermometer.

Check if there is a short circuit in the thermocouple sensor wiring.

Check if the thermocouple is broken.

If the above situation is normal, the thermocouple module of the channel shorted to see if the temperature is too different with the room temperature; a large difference between the need to see whether there is a heating element around the module, the module cooling environment is good.

How to set PID parameters

In engineering practice, the most widely used regulator control law for the proportion, integral, differential control, referred to as PID control, also known as PID regulation. PID controller has been nearly 70 years of history, it is its simple structure, good stability, reliable, easy to adjust and become one of the main technical control of industrial technology. When the structure and parameters of the controlled object can not be fully grasped or the precise mathematical model is not obtained, when the other techniques of the control theory are difficult to adopt, the structure and parameters of the system controller must be determined by experience and field debugging. PID control technology is the most convenient. That is, when we do not fully understand a system and the controlled object, or can not be effectively measured by means to obtain system parameters, the most suitable for PID control technology. PID control, in fact there are PI and PD control. PID controller is based on the system error, the use of proportional, integral, differential control to control the amount of control.

Proportional (P) control

Proportional control is one of the simplest controls. The output of the controller is proportional to the input error signal. When there is only proportional control, there is a steady state error (Steady-state error).

    Integral (I) control

In the integral control, the output of the controller is proportional to the integral of the input error signal. For an automatic control system, if there is steady-state error after entering steady-state, then the control system is said to have steady-state error or referred to as poor system (System with Steady-state Error). In order to eliminate the steady-state error, in the controller must be introduced "integral items" and "rdquo ;. The integral term for the error depends on the time integral, and as time increases, the integral term increases. In this way, even if the error is small, the integral term increases with time, which increases the output of the controller to further reduce the steady-state error until it is equal to zero. Therefore, the proportional + integral (PI) controller can make the system without steady state error after entering steady state.

   Differential (D) control

In differential control, the output of the controller is proportional to the differential of the input error signal (ie, the rate of change in error). Automatic control system in the process of overcoming the error may occur in the oscillation or even instability. The reason for this is that there is a large inertia component (link) or a delay component, which has the effect of suppressing the error, and the change is always behind the change of the error. The solution is to make the suppression of the role of error changes "ahead of" and that error is close to zero, the role of suppression error should be zero. That is to say, in the controller only the introduction of the proportion of the item is often not enough, the proportion of the role of the amplification is only the magnitude of the error, and the current need to increase the "differential" and it can predict the error So that the controller with proportional + derivative can make the control effect of the suppression error equal to zero or even negative, so as to avoid the serious overshoot of the controlled quantity. So for a larger inertia or lagged controlled object, the proportional + differential (PD) controller can improve the dynamic characteristics of the system during the adjustment process.

    In the PID parameters to set the time if you can have a theoretical way to determine the PID parameters of course is the most ideal method, but in practical applications, more is through the Minato method to determine the PID parameters.

    Increasing the scale factor P will generally accelerate the response of the system, in the case of static difference is conducive to reducing the static difference, but the excessive proportion of the system will have a relatively large overshoot, and produce oscillation, the stability of change Bad.

    Increasing the integration time I is advantageous in reducing the overshoot, reducing the oscillation, increasing the stability of the system, but the system static elimination time becomes longer.

    Increasing the derivative time D is helpful to speed up the response speed of the system, reduce the system overshoot and increase the stability, but the system can reduce the ability to suppress the disturbance.

    In the test, you can refer to the above parameters on the impact of the system control process trends, the implementation of the first adjustment of the proportion of the parameters, after the integral, and then the differential adjustment steps.

    First set the proportion of part. The proportional parameter is changed from small to large and the corresponding system response is observed until the response is fast and the overshoot is small. If the system has no static or static difference has been small to the allowable range, and the response curve has been satisfied, you only need to adjust the regulator.

    If the system on the basis of the adjustment of the static difference can not meet the design requirements, you must join the integral link. In the setting of the integration time will be set to a relatively large value, and then has adjusted the proportion of the coefficient is slightly reduced, and then reduce the integration time, making the system to maintain good dynamic performance, the static difference is eliminated. In this process, according to the system's response curve is good or bad to change the scale factor and integration time, in order to get a satisfactory control process and tuning parameters.

    If the process of adjustment in the process of repeated adjustment of the system can not get satisfactory results, you can join the differential link. First, the differential time D is set to 0, on the basis of the gradual increase in the differential time, while the corresponding change in the proportion of the coefficient and the integration time, step by step test, until a satisfactory adjustment effect.




Figure A: There is no overshoot of the response curve, the proportional coefficient P should be increased so that the response has a certain overshoot



Figure B: The overshoot of the response curve is too large and the scale factor P should be reduced to reduce the overshoot of the response.



Figure C: The response curve has a certain overshoot, but because the integration time is too long to cause the response can not be smooth, should reduce the integration time






Figure E: Ideal response curve.


Field wiring FAQ














备注: 如果所有的线(动力线及信号线)都用金属蛇皮来套,那效果会很好。





Wiring irregularity results in instability of the analog measurements


EM231 4AI × 12BIT or EM235 module measurement is not stable

the reason:

The module input negative terminal is not connected to the M terminal, causing the module to fail to effectively suppress the common mode voltage


Connect the negative input of the module to the M terminal.

The measured values for all channels of the thermocouple module are 217


The measured value of all channels of the EM231 TC / PID module is 32767

the reason:

32767 indicates that the input has been disconnected, the user may have used a non-isolated thermocouple, resulting in the input of the module due to accidentally string higher than 30V above the voltage and burned.


Using isolated thermocouple, or take other means to ensure that the input will not string into more than 30V high voltage.

124XP host, using the Siemens programming cable to download the program block prompt "non fatal error".

A: 124XP host, using the Siemens programming cable to download the program block prompt "non fatal error".

Q: The 100 series PLC does not support the Siemens programming cable. Also note that the number 100 series PLC timer counter can not exceed 127.

CTS7 231-7NF32, the last channel is not connected to PT100, the SF light on the module flashes.

A: CTS7 231-7NF32, the last channel is not connected to PT100, the SF flash on the module.

Q: The SF lamp flashes to indicate that the module has a channel disconnected. A 100 ohm resistor can be used to access the unused channel and eliminate the power alarm (SF lamp off).

COTRUST PLC power to keep data and time are?

First, the data power to maintain the length of time:


1, the use of built-in button batteries, about 1 year;

2, the use of permanent preservation, the data will be saved to the EEPROM, permanent preservation.


1, the use of built-in capacitor, about 100 hours;

2, the use of an external battery card, about 2 years;

3, the use of permanent preservation, the data will be saved to the EEPROM, permanent preservation.

CTH300 series: permanent preservation.

Second, the power to maintain data capacity:

CPU122, CPU222: 2048 bytes;

CPU124, CPU224: 8192 bytes;

CPUI126, CPUI226: 10240 bytes;

CTH300: C series has 32KB; H36 has 32KB, H35 has 16KB.

EM277A and COTRUST touch screen communication problems


Use the Division I only with a PPI communication port of the CPU, do not buy Siemens original cable in the case, how to achieve the same time with the host computer and touch screen communication?


Through the 200CPU and 277A connection, take the MPI protocol, MPI communication line at the end of the open 277A A, B two points, the other end touch the screen communication port, the CPU and the touch screen baud rate settings consistent, you can communicate, The EM277A dial address is the MPI slave address configured for the HMI. as the picture shows.



其他的注意事项与触摸屏与 CPU通讯一样。

此方案可解决客户用到我司主机 PPI通讯不够的情况,如用到我司  CPU224+或者 CPU224E,由于此 CPU只带一个  PPI通讯口,可选择此种方案一个  PPI口连电脑上下载程序/监控,另外,经过 EM277A的  RS485连  HMI组成  MPI网络。相比于使用西门子  S7-300编程电缆,需要用到总线转换器,且西门子 S7-300编程电缆昂贵,此种方案降低了带来方便的同时有效地降低了成本。

CTSC-200 and S7-300MPI communicates

Question: How do I implement MPI communication between CTSC-200 and S7-300?


Solution: CTSC-200 and S7-300 between the use of MPI communication, CTSC-200 PLC does not need to write any communication-related procedures, only need to exchange data to a continuous V storage area can be, The S7-300 needs to call the system functions X_GET (SFC67) and X_PUT (SFC68) in OB1 (or Timing Interrupt Organization Block OB35) to enable communication between S7-300 and CTSC-200. When SFC67 and SFC68 are called VAR_ADDR Parameters fill in the CTSC-200 data address area, where to fill in the P # DB1. × × × BYTE n corresponds to the CTSC-200 V storage area which VB × × to VB (× × + n) data area.

First of all, according to the hardware configuration of S7300, configure S7300 station in STEP7 and download, pay attention to CTSC-200 and S7-300 factory default MPI address is 2, so you must first modify one of the PLC station address, the example program will S7300 MPI address is set to 2, CTSC-200 address set 3, and separately to S7300 and CTSC-200 communication rate settings are consistent, can be set to 9.6K, 19.2K, 187.5K three baud rate, the example program Which selected the rate of 19.2K.

The example program calls the data read and write function blocks in OB1: SFC67 and SFC68, as shown below:




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