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Clean operating room air-conditioning Control System Design and Implementation

Print View , by: iSee ,Total views: 61 ,Word Count: 2701 ,Date: Thu, 7 May 2009 Time: 6:54 PM

0 Introduction

Clean as a hospital operating room to control one of the most demanding, and its a constant temperature and humidity control requirements. However, due to indoorsurgery, general lighting, etc. will have an impact on temperature and humidity, resulting in its operation it is very difficult to meet the required temperature and humidity requirements to maintain a constant, so temperature and humidity indicator is the clean operating room to control the most important indicators. Temperature directly affects the patients and medical staff comfort, and when the room humidity is greater than 60% of the time, the rate of bacterial growth would be greatly accelerated, bacteria from the control point of view, humidity control is also extremely important. This requires the operating room air-conditioning system to adjust algorithm based on the specific temperature and humidity, and operating in accordance with the corresponding settings on the panel to respond quickly to real-time control requirements. Here based on Siemens S7-224cn PLC and text constitute TD400C display control system.

l system control

1.1 Temperature control requirements

By setting the tube in the wind's temperature and humidity sensors detect body temperature back to the wind and temperature measurements of the analog signal to the PLC input. PLC will be measured through the operating room temperature and the temperature settings panel comparison and PID calculation, the results output to a corresponding analog output, such as chilled / hot water electric valve, through the control of its opening to achieve temperature control.

1.2 Humidity control

By setting the tube in the wind's temperature and humidity sensors detect one return air humidity and temperature measured by the signal sent to the PLC analog input. PLC will be measured by the humidity and moisture through the operating room panels and set the PID value calculation, the results output to a corresponding analog output. Mode in the winter on the humidifier through the electric control valve regulating the opening to achieve the purpose of humidity control. Model in the summer, the humidity control is not a humidifier opening of a single control, but the regulator valve and the heater to achieve an integrated PID control.

1.3 Wind pressure control

Process in accordance with the requirements of duct pressure required to maintain a certain value, to meet the medical requirements of the operating room. System through the inverter-driven blower in advance will meet the technological requirements of the converter when the values of the frequency settings, will be set up in the air return duct pressure sensor measured the pressure value as a feedback value, calculated through the PID control inverter output frequency, so as to achieve pressure control.

1.4 man-machine interface requirements

Process in accordance with the requirements of the scene in the operating room with an operation panel, you can set the temperature and humidity control system and start and stop, at the same time have a panel of real-time temperature and humidity display; Similarly, the cabinet is installed in the control of man-machine interface TD400C through TD400C temperature and humidity can also set start and stop units. For the purpose of debugging the system, set up in TD400C compulsory mode, and manual settings return air temperature and humidity, shielding alarm signal.

TD400C priority higher than the operating room control settings panel can be shielded from the operating room setting signal.

1.5 security requirements

Fault in the system there are three kinds of signals are sent to signal fan failure, lack of wind protection fault signal, pressure signals in effect. Three kinds of signals that are aimed at the protection of air duct ventilation. Have a sound and light show alarm to remind staff to take measures.

2 System hardware and technology profile

2.1 Hardware components

By testing the entire system of hardware components, control components and implementation components.

Road in the wind by setting the temperature and humidity sensors to detect one return air temperature and humidity; by setting the pipe duct in the return air pressure sensors detect pressure; by setting the temperature of the water pipes on the water temperature sensor to detect and to determine the operating mode; mainly refers to control components S7-224 PLC, TD400C and operating room control panel; the implementation of electrical components including the control valve to the pipe, humidifier and heater control valve regulating valve and so on.

2.2 Technology Introduction

After system startup, such as the absence of lack of wind protection alarm signal is sent through pipes installed in the sensor system detection mode of the water temperature. Mode is divided into winter and summer. If the delivery pipes for the water temperature is greater than 30 ℃ in winter mode, which is lower than 30 ℃, compared with the summer pattern.

Mode in the winter, the temperature is lower than if the return air temperature, then open the valve actuators, flow more to raise the temperature of hot water; if the return air humidity lower than the set humidity, the humidifier opening open to raise the humidity. Mode in the winter if the return air temperature is higher than set value, the valve actuator to reduce the output aperture; usually in the winter mode is always lower than the return air humidity humidity settings, it does not consider the return air humidity possible to set the humidity. In the summer mode, the control is in addition to temperature dehumidifier. Priority requirements of the system and humidity regulation. The so-called priority conditioning and humidity means a higher humidity in summer time, after the controller by calculating the adjustment of the opening delivery pipes (tubes is about 7 ℃ chilled water) to achieve the purpose of cooling dehumidification, and the resulting temperature difference through the open electric heater to compensate. When the return air humidity set to meet the requirements, the system automatically enter a state of temperature control. Mode of choice flow chart shown in Figure 1.

Clean operating room air-conditioning Control System Design and Implementation

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3 system software design

In accordance with process requirements and hardware configuration using Siemens STEP7 MICRO/WIN32 system software configuration and design of man-machine interface TD400C.

Software design including temperature and humidity control, compulsory mode selection, mode selection and the police to deal with failure.

3.1 Mode Selection

Control mode is set is referring to the system is divided into TD400C control settings (manual) and the operating room control panel settings (automatic) two. In manual mode and pattern of coercive and non-mandatory. In manual mode can be set up panel shielding the operating room temperature, humidity and the system start and stop signals. Considerations for system debugging, the system also set up a mandatory mode. In the compulsory mode, you can manually set the return air temperature, return air humidity, air pressure sensors to the signal, and a variety of failures can be manually reset alarm signal, the control mode selection flow chart shown in Figure 2.

Clean operating room air-conditioning Control System Design and Implementation

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3.2 to deal with failure alarm

In accordance with the design requirements, if there is fault signal blower, lack of wind protection fault signal, pressure signal in effect, there will be sound and light show, to remind staff to take measures, the flow chart shown in figure 3.

Clean operating room air-conditioning Control System Design and Implementation

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3.3 Temperature and Humidity Control

Software design is the core of the temperature and humidity control, the use of PID control to regulate temperature and humidity. Control refers to the PID closed-loop control system PID control.

Conventional PID control system block diagram shown in Figure 4.

Clean operating room air-conditioning Control System Design and Implementation

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Is a linear PID controller, which in accordance with a given value of r (t) and the actual output value y (t) constitutes a control error:

e (t) = r (t) 1 y (t)

The deviation of the ratio of (P), integral (I) and differential (D) through a certain amount of linear combination of composition control u (t) of the control object. Its control law as follows:

Clean operating room air-conditioning Control System Design and Implementation

Picture not clear? Click here to view the image (larger).

Type in: KP proportional coefficient; TI for the integral time constant, TD for the differential time constant.

When the volume control between the target and detection of errors (or known as the control error), the error small, the volume of operations on the small, the greater the error, the greater the amount of operation, the control algorithm contains the ratio of deviation, or P action. With self-balancing of the purposes of the ratio of the control object to control the final stage of its step-by-step changes in a certain degree of error will be left behind, known as the steady-state error or offset. Control algorithm so that the error contained in the ratio of points to eliminate the steady-state error, or I move. Bias is reflected in the increase or decrease in volume of operations, in order to improve the control characteristics, it contains a control algorithm so that error of differential ratio, or D action, as a pre-action. Include the control of the three movements is the PID control algorithm.

Style (1) can also be written:

Clean operating room air-conditioning Control System Design and Implementation

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Where: KI = KP / TI for the integral coefficient; KD = KP TD for the differential coefficient.

Taking into account the charged object has a large hysteresis, and the PLC is a digital processing, the type (2) discretization of a:

Clean operating room air-conditioning Control System Design and Implementation

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Where: θ representative of the sampling period, e (k) on behalf of the error at the moment, e (k-1) on behalf of the last sampling period error. If θ small enough, this approximation can be quite accurate, was charged with continuous process and is very close to the control process. This algorithm is called the location algorithm. Algorithm because of the location of the whole output, so the output of each state with the past, and the calculation to the e (k) to accumulate, the computing workload. Moreover, because the computer output u (k) correspond to the actual location of the executing agency, such as computer failure, u (k) substantial changes in the location of the executing agency will cause significant changes in the production of such a situation is often the practice of in not allowed. Taking into account both the object of the system control valve, so the use of incremental PID control algorithm is better.

The type (3) in accordance with the principle of recursive push:

Clean operating room air-conditioning Control System Design and Implementation

Picture not clear? Click here to view the image (larger).

Style (5) as the incremental PID algorithm.

As the control increment △ u (k) only with the recent determination of the sampling times the value of k, and that was easier to get through the weighted effect of better control.

Control requirements in accordance with the scene, was charged with the process can not overshoot overshoot phenomenon that is emerging. However, the construction site and the combination of temperature, humidity has a large time delay characteristics inevitably overshoot.

The quality of temperature control is a decisive aspect of temperature control parameters of PID regulator tuning, PID parameter setting determines the quality of the quality of temperature control. In practice, the hospital operating room temperature of hope as far as possible, fast settling time. However, the rapid response to temperature, this will result in overshoot, and is likely to form a long-term temperature shocks. Adjust the speed of temperature control accuracy and temperature are often irreconcilable, if permitted under the premise of accuracy to speed up the adjustment speed as much as possible means to reduce the shock. Usual practice is in the process PID regulator to regulate the introduction of dead-zone control. However, even if the protection of the dead zone, it is subject to site conditions, the effect does not have universality.

Er, if set for the temperature error, Es settings for temperature, Eb actual values for temperature, Et for the temperature of the dead zone, then:

Clean operating room air-conditioning Control System Design and Implementation

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The consequences of this is that, even if the introduction of a dead zone, the effect on the improvement of PID regulator is also limited. To this end, the introduction of the rate of temperature change, through changes in the rate of temperature change to artificially change the dead zone, so that errors in calculating the value of PID would be changed to regulate the speed will change accordingly.

Set up for one minute prior to T1 the temperature, T2 is the temperature at this time, Tc is the rate of change of temperature, Tc = T2 is a T1. Tc not only able to determine, through the rise and fall of temperature change, can know the speed of temperature change.

Thus, the use of Tc and the current temperature of the actual Eb error Es a dead zone to set the temperature.

If Es-Eb> 0 that does not meet the temperature setting and Tc> 1, then the Et = | Es-Eb |, that is, PID temperature regulation, the error Er enter zero, then stop PID temperature regulation , so that automatically increase the temperature to set the value. And vice versa.

4 Conclusion

Clean operating room for the control requirements, the establishment of a S7-224PLC as control core, and as a man-machine interface TD400C control system. Through the system to meet the operating room to control temperature and humidity, the maximum extent to avoid the overshoot phenomenon, the whole system to improve the controllability and stability.


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