User Guide - Eurotherm Ltda

More documents

Recommendations

Info

nanodac RECORDER/CONTROLLER: USER GUIDEB2.2 TYPES OF CONTROL LOOPB2.2.1 On/Off controlThis form of control turns heating power on when the process value is below the setpoint, and turns it offwhen it is above the setpoint (see also figure B2.6.9a). If cooling is configured, it has its own relay which operatesin a similar way. In Direct Acting mode, the behaviour is inverted. On/off is suitable for controllingswitching devices such as relays.Because of the thermal inertia of the load, a certain amount of oscillation will take place, and this can affectthe quality of the product. For this reason, On/Off control is not recommended for critical applications.Depending on the nature of the process being controlled, some hysteresis may have to be included to preventcontinuous operation or chatter in the controlling device.B2.2.2 PID ControlAlso known as ‘three term control’, this type of control continuously adjusts the output demand, accordingto a set of rules, in order to control the process as closely as possible to requirements. PID provides morestable control than On/Off control but is more complex to set up as the parameters must match the characteristicsof the process under control.The three major parameters are: Proportional band (PB), Integral time (Ti) and Derivative time (Td) and theoutput from the controller is the sum of these three terms. This output is a function of the size and durationof the error value and the rate-of-change of the process value.It is possible to disable the integral and/or derivative terms and control on proportional only, on proportionalplus integral (PI) or proportional plus derivative (PD).PI control is often used when the PV is noisy and/or subject to rapid variations, where derivative action wouldcause the output power to fluctuate wildly.PROPORTIONAL BANDThe proportional band (PB) delivers an output which is proportional to the size of the error signal. It is therange over which the output power is continuously adjustable in a linear fashion from 0% to 100% (for a heatonly controller). Below the proportional band the output is full on (100%), above the proportional band theoutput is full off (0%) as shown in figure B2.2.2a.The width of the proportional band determines the magnitude of the response to the error. If PB is too narrow(high gain) the system oscillates; if it is too wide (low gain) control is sluggish. The ideal situation is whenthe proportional band is as narrow as possible without causing oscillation.Figure B2.2.2a also shows the effect of narrowing proportional band to the point of oscillation. A wide proportionalband results in straight line control but with an appreciable initial error between setpoint and actualtemperature. As the band is narrowed the temperature gets closer to setpoint until eventually, itbecomes unstable.The proportional band may be set in engineering units or as a percentage of the controller range.WideNarrowProportionalbandSetpointOutputTemperatureIncreasingproportional bandSP Temperature TimeFigure B2.2.2a Proportional band action (reverse acting)Appendix BPage 300HA030554Issue 7 Nov 12
nanodac RECORDER/CONTROLLER: USER GUIDEB2.2 TYPES OF CONTROL LOOP (Cont.)INTEGRAL TERMIn a proportional only controller, as seen in the previous section, an error must exist between setpoint andPV in order for the controller to deliver power. Integral is used to achieve zero steady state control error.The integral term slowly modifies the output level as a result of any error between setpoint and measuredvalue. If the measured value is below setpoint the integral action gradually increases the output in an attemptto correct the error. If it is above setpoint integral action gradually decreases the output or increasesthe cooling power to correct the error.Figure B2.2.2b shows proportional plus integral action.SPTemperatureTimeFigure B2.2.2b: Proportional + Integral ControlThe integral term is set in seconds. The longer the integral time constant, the more slowly the output is modifiedand the more sluggish the response. Too small an integral time causes the process to overshoot, andperhaps to start oscillating. The integral action may be disabled by setting its value to Off.DERIVATIVE TERMDerivative (or rate) action provides a sudden change in output linked to the rate of change in error, whetherthis is caused by PV alone (derivative on PV) or by a change in the SP as well (derivative on error selection).If the measured value falls quickly, derivative provides a large change in output in an attempt to correct theperturbation before it goes too far. It is most beneficial in recovering from small perturbations.SPTemperatureTimeFigure B2.2.2c Proportional + Integral + Derivative ActionDerivative is used to improve the performance of the loop. There are, however, situations where derivativemay be the cause of instability. For example, if the PV is noisy, then derivative can amplify that noise andcause excessive output changes, in these situations it is often better to disable the derivative and re-tune theloop.HA030554Issue 7 Nov 12Appendix BPage 301
Page 1 and 2:
nanodacUser Guidenanodac recorder/c
Page 3:
Declaration of ConformityManufactur
Page 6 and 7:
nanodac RECORDER/CONTROLLER: USER G
Page 8 and 9:
Page 10 and 11:
Page 12 and 13:
Page 14 and 15:
Page 16 and 17:
Page 18 and 19:
Page 20 and 21:
Page 22 and 23:
Page 24 and 25:
Page 26 and 27:
Page 28 and 29:
Page 30 and 31:
Page 32 and 33:
Page 34 and 35:
Page 36 and 37:
Page 38 and 39:
Page 40 and 41:
Page 42 and 43:
Page 44 and 45:
Page 46 and 47:
Page 48 and 49:
Page 50 and 51:
Page 52 and 53:
Page 54 and 55:
Page 56 and 57:
Page 58:
Page 62 and 63:
Page 64 and 65:
Page 66 and 67:
Page 68 and 69:
Page 70 and 71:
Page 72 and 73:
Page 74 and 75:
Page 76 and 77:
Page 78 and 79:
Page 80 and 81:
Page 82 and 83:
Page 84 and 85:
Page 86 and 87:
Page 88 and 89:
Page 90 and 91:
Page 92 and 93:
Page 94 and 95:
Page 96 and 97:
Page 98 and 99:
Page 100 and 101:
Page 102 and 103:
Page 104 and 105:
Page 106 and 107:
Page 108 and 109:
Page 110 and 111:
Page 112 and 113:
Page 114 and 115:
Page 116 and 117:
Page 118 and 119:
Page 120 and 121:
Page 122 and 123:
Page 124 and 125:
Page 126 and 127:
Page 128 and 129:
Page 130 and 131:
Page 132 and 133:
Page 134 and 135:
Page 136 and 137:
Page 138 and 139:
Page 140 and 141:
Page 142 and 143:
Page 144 and 145:
Page 146 and 147:
Page 148 and 149:
Page 150 and 151:
Page 152 and 153:
Page 154 and 155:
Page 156 and 157:
Page 158 and 159:
Page 160 and 161:
Page 162 and 163:
Page 164 and 165:
Page 166 and 167:
Page 168 and 169:
Page 170 and 171:
Page 172 and 173:
Page 174 and 175:
Page 176 and 177:
Page 178 and 179:
Page 180 and 181:
Page 182 and 183:
Page 184 and 185:
Page 186 and 187:
Page 188 and 189:
Page 190 and 191:
Page 192 and 193:
Page 194 and 195:
Page 196 and 197:
Page 198 and 199:
Page 200 and 201:
Page 202 and 203:
Page 204 and 205:
Page 206 and 207:
Page 208 and 209:
Page 210 and 211:
Page 212 and 213:
Page 214 and 215:
Page 216 and 217:
Page 218 and 219:
Page 220 and 221:
Page 222 and 223:
Page 224 and 225:
Page 226 and 227:
Page 228 and 229:
Page 230 and 231:
Page 232 and 233:
Page 234 and 235:
Page 236 and 237:
Page 238 and 239:
Page 240 and 241:
Page 242 and 243:
Page 244 and 245:
Page 246 and 247:
Page 248 and 249:
Page 250 and 251:
Page 252 and 253:
Page 254 and 255:
Page 256 and 257:
Page 258 and 259:
Page 260 and 261:
Page 262 and 263: nanodac RECORDER/CONTROLLER: USER G
Page 348 and 349: NANODAC RECORDER/CONTROLLER: USER G
Page 362 and 363:
NANODAC RECORDER/CONTROLLER: USER G
Page 364 and 365:
Page 366 and 367:
Page 368 and 369:
Page 370 and 371:
Page 372 and 373:
Page 374 and 375:
Page 376 and 377:
Page 378 and 379:
Page 380 and 381:
Page 382 and 383:
Page 384 and 385:
Page 386 and 387:
Page 388 and 389:
Page 390 and 391:
Page 392:
show all

User Guide - Eurotherm Ltda

Create successful ePaper yourself

Delete template?

Save as template?