Siemens SIMATIC S5 Manual

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Description of the FirmwareIP244C79000–B8576–C860–024–8To obtain a temperature related to 0 C, the reference junction is acquired asUTH 2 = K T 2 and is included in UTh.The temperature compensation is performed via a Pt 100 resistance thermometer with which thereference junction temperature is read in at the beginning of each cycle. The Pt 100 at channel 15is also checked for line break. If a line break or a temperature > 60 C is detected, an error bit isset (message 16, byte 2). In this case, the value of the ambient temperature before the error wasdetected is used for further calculation. If the error occurs immediately after parameter assignment,the ambient temperature 0 C (= 32 F) is used.To indicate the actual value, a filter can be looped into the signal path. If this is required, appropriateparameters must be assigned. The actual value is displayed with a time delay after averaging eightvalues.If more than 1024 or 2048 encoding units (or 3997 encoding units in pure Pt 100 operation and 1536encoding units with the special function) are read in, the actual value is limited to the maximumvalue. The actual values can be represented either as binary or BCD coded values as required. Theactual values are stored in message 17.If BCD coding is required, the values are stored as follows:S5 formatAddress n: thousands hundredsAddress n + 1: tens units1.1.3 Manipulated Variable Processing, Outputs-Heating SwitchThe module has 17 digital control outputs for the 13 controllers. This means that nine 2-stepcontrollers and four 3-step controllers or a maximum of eight 3-step controllers and one 2-stepcontroller can be configured (control byte 1).Depending on the configuration, the outputs of 2 or 3-step controllers are assigned to the inputsinternally by the firmware. If, for example, three controllers are configured as 2-step controllers withinput channels 0, 1 and 2, the manipulated variables are output at outputs 17, 16 and 15respectively. If a 3-step controller is configured as the fourth controller with input channel 3, themanipulated variable (e.g. heating, cooling) will then be output at outputs 14 and 13.The manipulated variable calculated from the control algorithm forms a 2 or 3-step signal dependingon the configuration. With the pulse-duration modulation (percentage output), the manipulatedvariable (heating or cooling) is only output for the part of the sampling time (TA) which correspondsto the calculated value of the controller output signal. The smallest ON interval is 50, 55, 60 or 80 msdepending on the parameter assignment (see Operating Instructions in this manual, Section 3.4.2).At a sampling time of 10 s, for example, a resolution of maximum 0.5% is achieved at an ON intervalof 50 ms. To suppress short ON or OFF times, a response threshold can also be input.