The 5th PSU-UNS International Conference on Engineering and Technology (ICET-2011), Phuket, May 2-3, 2011

Prince of Songkla University, Faculty of Engineering Hat Yai, Songkhla, Thailand 90112

Abstract: This paper presents using industrial networked control system (NCS) for operating pressure tank system to control pressure variable and flow variable simultaneously. Advantage of the resources provided by industrial NCS is implemented to operate and control the pressure tank system such as programming, control algorithm with tuning parameters, human machine interface, and alarm management system together with a tool for commissioning a field instruments. A simple function block of proportion-integral-derivative (PID) controller is applied to control pressure variable and flow variables with simple structure. The PID parameters are tuned by PID-tunner. Performance of control loops with the mentioned tuning procedure is evaluated to show operation with each condition. The evaluated performance is good enough in a basic laboratory course for instrumentation and control engineering undergraduate students at King Mongkut’s Institute of Technology Ladkrabang (KMITL). Key Words: Networked Control System (NCS), Profibus DP and PA, Process Control System 7 (PCS7), Pressure Tank System.

1. INTRODUCTION Nowadays, industrial networked control system

(NCS) continuously developed from distributed control system (DCS) are becoming popular because a field bus for process control such as PROFIBUS DP and PA and foundation field bus (FF H1) is being used to replace HART protocol in industrial complex process for process automation (PA). For factory automation (FA), the old protocol is replaced by industrial Ethernet such as PROFINET from Siemens, EtherCAT from Beckhoff, etc. Also problem of stability of control method caused from delay in network is discussed more but the most of report about NCS is still not really implement. Basic control method with tuning method and gain scheduling such as PID controller for single loop control and advantage control method such as model predictive control (MPC) for multivariable control, fuzzy logic control tool are provided by many vendors such as

Siemens, Emerson, Yokogawa, Honeywell, and etc. To real implement with first basic control method together with tuning method of industrial networked system, PCS 7 from Siemens [1] is implemented in our laboratory with process control, pressure tank system by using separated two loop PI controller. SMAR field instrument IF303 and FI303 [4] as PROFIBUS PA protocol is used to interface with original instrument.

This paper is organized as follows. In section 2, pressure tank system is briefly described both process and control system configuration. Commissioning of field instrument is described in Section III. In Section 5, control method and tuning together with PROFIBUS PA input-output function is described. Experimental results and conclusions are shown and discussed in Section 5 and 6, respectively.

2. PRESSURE TANK SYSTEM

2.1. Brief description of the Process

Fig. 1 shows diagram of pressure tank system, setted up in our laboratory, comprising of three parts. First part is water supply consisting of storage water tank, water pump with inverter to control speed of induction motor, and surge tank with pressure transmitter (PT1, range : 0-100 psi, output : 4-20 mA) as feedback pressure signal to inverter for controlling pressure value in surge tank. Second part is pressure control consisting of pressure tank, control valve (CV1, range : 0-100 %, input : 4-20 mA), and pressure transmitter (PT2, range : 0-60 psi, output : 4-20 mA). Third part is flow control consisting of control valve (CV2, range : 0-100 %, input : 4-20 mA) and flow transmitter (FT1, range : 0-40 l/m, output : 4-20 mA).

2.2. Control System Configuration

To implement industrial networked control system, control system architecture as PCS 7 from Siemens [1] is comprising of automation station (AS), engineering station (ES), and operator station (OS). SMAR field instruments are used as field bus with PROFIBUS DP/PA coupler. Fig. 2 (a) shows hardware configuration

USING A INDUSTRIAL NETWORKED CONTROL SYSTEM FOR PRESSURE

TANK SYSTEM Sakreya Chitwong, Pawin Komolviphat, and Fusak Cheevasuvit

School of Instrumentation and Control Engineering, Faculty of Engineering King Mongkut’s Institute of Technology Ladkrabang, Bangkok, 10520 THAILAND

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by STEP 7 in HW Conf. AS consists of universal rack UR2, power supply PS407, CPU 414-3 DP V3.1 for PCS 7 V7.1, and CP443-5 ext PROFIBUS DP master for connection to OS. ES is used for hardware configuration, control programming development, and field device configuration. PROFIBUS DP master system (1) of the CPU 414-3 DP in AS is used to connect with PROFIBUS DP/PA coupler FDC 157-0 for linking with field devices SMAR IF303 (current 4-20 mA to PROFIBUS PA signal) and SMAR FI303 (PROFIBUS PA signal to current 4-20 mA). Fig. 2(b) shows connection between AS, namely SIMATIC 400(1), OS, namely SIMATIC PC STATION(1) with WinCC application as human machine interface (HMI) and CP5611 for linking to CP443-5 ext via PROFIBUS DP master system (2), and field device with the transparency coupler by STEP7 in NetPro.

3. COMMISSIONING FIELD INSTRUMET The first step to use a PROFIBUS PA field

instrument is configurating its parameter to corresponding with a controlled process. SMAR IF303 and FI303 [4] are used to convert 4-20 mA current from a original instrument (pressure and flow transmitter) to PROFIBUS PA signal and PROFIBUS PA signal to 4-20 mA current for a original control value, respectively. Both the IF303 and FI303 is configurated by PDM program from Siemens. Second and third channel of IF303 is connected to PT2 and FT1, respectively. Analog input block as function block of IF303 is configurated for 4-20mA to 0-60 psi and to 0-40 l/m, PROFIBUS PA signal, respectively. Second and third channel of FI303 is connected to CV1 and CV2, respectively. Analog output block as function block of FI303 is configurated for 0-100 % PROFIBUS PA signal to 4-20mA.

4. PID CONTROL TUNING Standard PID control function, namely CTRL_PID,

input and output function for PROFIBUS PA, namely PA_AI and PA_AO, in PCS7 libraries for CFC [2] is applied. Fig. 3 shows all of the CFC block for our control program consisting of two PA_AI input function, two PA_AO output function, and two CTRL_PID control function for pressure and flow control. To tuning CTRL_PID control function, PCS7-tunner [3] is separately employed. The CTRL_PID control function for flow control (FIC) is firstly tuned by letting CV1 operate of 100% and running PCS7-tunner until getting PID parameters shown in Table 1 seeing that the flow controller is PI controller only. Next, the CTRL_PID control function for pressure control (PIC) is tuned by letting fixed flow value set point SP_F of 25 l/m and running PCS7-tunner until getting PID parameters shown in Table 1. The pressure controller being the same as the flow control is PI controller. By using the PCS7-tunner, the model type of both flow and pressure process is in first order.

Table 1. Parameter of PID controller for flow and pressure control

Controller Flow control Pressure control PID

Gain 3.522 0.428 Reset time 38.9 37.116

Derivative time 0 0 For our pressure tank system, operating points is

shown in Table 2. Table 2. Operating points of the pressure tank system

Control Loop Operation points Units FIC 0-40 Liters/min PIC 0-60 Psi

5. EXPERIMENT RESULTS Experimental tests were carried out to evaluate PID

controller with a separated two loops by utilizing continuous function chart (CFC). The sampling time is of 100 ms. For pressure tank system, two PI controllers with PCS7 PID-tunner are implemented. By using our setup system shown in Fig. 1, Fig. 4, 5 and 6 show the experimental results with three conditions. First the fixed set point of pressure is of 40 psi and varying flow rate from 15 to 30 l/m. Seeing in Fig. 4 shows that the pressure value is decreased because flow value is increased and back to the set point again, the flow value can precisely reach to the set point. Second the fixed set point of flow value is of 30 l/m and varying pressure from 40 to 30 psi. Seeing in Fig. 5 shows that the pressure can precisely reach to the set point, but flow value is decreased because of increased pressure and back to the set point again. Final varying pressure and flow value is from 30 to 20 l/m firstly and 30 to 40 psi, respectively. Result of performance of controller shown in Fig. 6 is the same as previous two conditions.

6. REFERENCES This is first report for instrumentation and control

engineering undergraduate students to study the industrial networked control system environment. Not only now advantage control method is not implemented, but also the basic PID control function with tunner implemented shows performance good enough.

7. ACKNOWLEDGEMENT The authors thank Mr. Narupon Panakulchiwit from

Siemens (Thailand) Co., Ltd. for their support of this project.

8. REFERENCES [1] Siemens AG A&D AS CS 2 PA Systems Support Process

Automation and A&D AS MP 7 Marketing & Promotion SIMATIC PCS7, SIMATIC PCS7 on Tour – Basic, Siemens AG, Karlsruhe, Germany, March 2007.

[2] Siemens AG, SIMATIC CFC for S7 Continuous Function Chart, Siemens AG, Karlsruhe, Germany, 2003.

[3] Siemens AG, SIMATIC PCS7 PID Control with Gain Scheduling and PID Tuning, Siemens AG, Germany, 2009.

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[4] SMAR, IF303 and FI303 Operation & Maintenance Instruction Manual, 2007.

Fig. 1 Diagram of pressure tank system.

(a)

(b)

Fig. 2 (a) Hared ware configuration in HW Conf (b) Connection in NetPro

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Fig. 3 CFC programming for control, input, and output.

Fig. 4 Respond of fixed pressure variable (40 psi) and varied flow variable (15 to 30 l/min).

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Fig. 5 Respond of varied pressure variable (40 to 30 psi) and fixed flow variable (30 l/min).

Fig. 6 Respond of varied pressure variable (30 to 40 psi) and varied flow variable (30 to 20 l/min).

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