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REAL value restricted to 32768.0?

Created by: roverman at: 7/4/2018 11:31 AM (7 Replies)

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7/4/2018 11:31 AM	Rate (0)
roverman Experienced Member Joined: 1/30/2013 Last visit: 1/16/2026 Posts: 22 Rating: (2)	Hello, I recently discovered that several of our "running hours" counters (REAL value) have stopped at 32768, when I look in the DB I see that the actual value is 32768.0 and not increasing. I can modify them to a higher value but they won't increase, if I set it to a lower value they start to increase again. The logic is in an FC with an IN/OUT REAL "WORK_HOUR", when drive is active and a pulse signal "3.6 sec" is on the value is increased by 0.001 (3.6 x 1000 = 1 hour). Can someone explain why this would stop working at this value? And how would you suggest to work around this and still keep a high resolution in the monitoring? Best regards Ronnie

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7/4/2018 12:26 PM	Rate (0)
jacek d Platinum Expert Joined: 9/23/2005 Last visit: 1/20/2026 Posts: 5155 Rating: (772)	Looks like you have so-called rounding error (which in fact is not an error but expected behaviour). Some nice reading for you. BTW, if you place your code here we may check it to see if it is not something else.
	Regards, Jacek What is confusing you is the fact that you never see a number but always its digit representation. So you end up thinking that the number is the representation. - Andrej Bauer Any claims against me - based on whatever legal reason - resulting from the use of any code and/or ideas presented on this forum shall be excluded. #StayWithUkraine
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This contribution was helpful to 2 thankful Users roverman crazyCow

7/4/2018 1:09 PM	Rate (0)
roverman Experienced Member Joined: 1/30/2013 Last visit: 1/16/2026 Posts: 22 Rating: (2)	Thank you for providing som information on the subject, I guess there are some pitfalls when working with floating values . I'm now thinking I might need a separate value to store part of hour and just use whole hours in the value presented to HMI... Here's the code, run time is in the last network before SET/SAVE. FUNCTION "Cmp_VSD" : VOID TITLE =CM02 - Motor VERSION : 0.1 VAR_INPUT I_MCCRdy : BOOL ; //Input: MCC Ready I_Maint : BOOL ; //Input: Maintenance Switch I_Therm : BOOL ; //Input: Thermal Protection RunEnb : BOOL ; //Run Enable LocSel : BOOL ; //Local Selected LocStart : BOOL ; //Local Strat Command LocStop : BOOL ; //Local Stop Command Auto_ON : BOOL ; //Automatic On Command Reset : BOOL ; //Reset Alarm Command CmdMan : BOOL ; //Command Manual CmdAuto : BOOL ; //Command Automatic CmdStart : BOOL ; //Command Start CmdStop : BOOL ; //Command Stop END_VAR VAR_OUTPUT S_LOC : BOOL ; //Local Mode Selected S_MAN : BOOL ; //Manual Mode Selected S_AUTO : BOOL ; //Automatic Mode Selected S_RUN : BOOL ; //Running Status S_RDY : BOOL ; //Ready Status END_VAR VAR_IN_OUT CTRL : "VSD"; //Control Aux. Structure A_MCC_RDY : BOOL ; //Alarm MCC Ready A_RUN_TOUT : BOOL ; //Alarm Run Timeout A_MAINT : BOOL ; //Alarm Maintenance A_THERM : BOOL ; //Alarm Trermal Protection WRK_HOUR : REAL ; //Working Hours END_VAR VAR_TEMP T_RunCmdChgd : BOOL ; T_FbckAlmDlyd : BOOL ; Alarm : BOOL ; END_VAR BEGIN NETWORK TITLE =Manual mode A( ; O #CmdMan; O #CTRL.ManReq; ) ; AN #CmdAuto; = #CTRL.ManReq; NETWORK TITLE =Operation mode A "ONE"; = L 1.0; A L 1.0; A #LocSel; = #S_LOC; A L 1.0; AN #LocSel; A #CTRL.ManReq; = #S_MAN; A L 1.0; AN #LocSel; AN #CTRL.ManReq; = #S_AUTO; NETWORK TITLE =Run command A #RunEnb; A( ; A #S_AUTO; A #Auto_ON; O ; A #S_MAN; A( ; O #CmdStart; O #CTRL.RUN_REQ; ) ; AN #CmdStop; O ; A #S_LOC; A( ; O #LocStart; O #CTRL.RUN_REQ; ) ; AN #LocStop; ) ; = #CTRL.RUN_REQ; NETWORK TITLE =Run command status changed A "ONE"; = L 1.0; A L 1.0; A( ; A #CTRL.RUN_REQ; AN #CTRL.Aux_RunCmd; O ; AN #CTRL.RUN_REQ; A #CTRL.Aux_RunCmd; ) ; = #T_RunCmdChgd; A L 1.0; A #CTRL.RUN_REQ; = #CTRL.Aux_RunCmd; NETWORK TITLE =Feedback timeout alarm A "ONE"; = L 1.0; A L 1.0; A #T_RunCmdChgd; JNB _001; L 30; T #CTRL.RunFdbkTm; _001: NOP 0; A L 1.0; A( ; L #CTRL.RunFdbkTm; L 0; <=I ; ) ; = #T_FbckAlmDlyd; A L 1.0; AN #T_FbckAlmDlyd; JNB _002; L #CTRL.RunFdbkTm; L "OB_DB_TimeClock".OB1_Time_100ms; -I ; T #CTRL.RunFdbkTm; _002: NOP 0; NETWORK TITLE =Feedback tiemout alarm A( ; A #T_FbckAlmDlyd; A( ; A #CTRL.RUN_REQ; AN #CTRL.RUN_FBK; O ; AN #CTRL.RUN_REQ; A #CTRL.RUN_FBK; ) ; O ; A #A_RUN_TOUT; AN #Reset; ) ; A "ZERO"; = #A_RUN_TOUT; NETWORK TITLE =MCC ready alarm ON #I_MCCRdy; O ; A #A_MCC_RDY; AN #Reset; = #A_MCC_RDY; NETWORK TITLE =Maintenance switch alarm ON #I_Maint; O ; A #A_MAINT; AN #Reset; = #A_MAINT; NETWORK TITLE =Thermal protection alarm ON #I_Therm; O ; A #A_THERM; AN #Reset; = #A_THERM; NETWORK TITLE =Statuses to HMI A "ONE"; = L 1.0; A L 1.0; A #CTRL.RUN_REQ; A #CTRL.RUN_FBK; = #S_RUN; A L 1.0; A( ; O #A_RUN_TOUT; O #A_MCC_RDY; ) ; = #Alarm; A L 1.0; AN #Alarm; = #S_RDY; NETWORK TITLE =Operation hours A #CTRL.RUN_REQ; A "OB_DB_TimeClock".Pulse.P3_6secONS; JNB _003; L #WRK_HOUR; L 1.000000e-003; +R ; T #WRK_HOUR; _003: NOP 0; NETWORK TITLE =Save RLO SET ; SAVE ; END_FUNCTION Best regards Ronnie

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7/4/2018 4:09 PM	Rate (1)
jacek d Platinum Expert Joined: 9/23/2005 Last visit: 1/20/2026 Posts: 5155 Rating: (772)	So you have exactly problem with rounding error. One solution is to use dint variable as a counter and increase it every time interval. And then derive your readout out of it. In your case (3.6 sec) it should be enough for 240 working years.
	Regards, Jacek What is confusing you is the fact that you never see a number but always its digit representation. So you end up thinking that the number is the representation. - Andrej Bauer Any claims against me - based on whatever legal reason - resulting from the use of any code and/or ideas presented on this forum shall be excluded. #StayWithUkraine
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7/4/2018 4:35 PM	Rate (0)
roverman Experienced Member Joined: 1/30/2013 Last visit: 1/16/2026 Posts: 22 Rating: (2)	Yes, it would seem so. I got the same results when I tried it in PLCSIM, I also noticed that the value seems to drift a bit when adding fractions so it isn't perfect for keeping track of time. Since our HMI is set up for floating point values I will create an accompanying INT to keep track of part of an hour and only update on whole hours. Filling in all those variables for the new FC will be fun... Thanks again! Best regards Ronnie

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7/4/2018 5:08 PM	Rate (0)
#dP Posts: 2826 Rating: (692)	Hi Ronnie. Why not just add the DINT and leave the REAL as is. Add 1 to the DINT just like you are adding the 3.6sec now. Then have #WRK_HOUR := DINT_TO_REAL(#DINT_VALUE) * 0.001 From the HMI point of view, nothing changed. BR
#dP Posts: 2826 Rating: (692)
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7/5/2018 10:46 AM	Rate (0)
roverman Experienced Member Joined: 1/30/2013 Last visit: 1/16/2026 Posts: 22 Rating: (2)	I guess that would work as well as using an INT for the part of hour, but I would still need to do a new FC to be able to feed the new DINT variable or am I missing something here? Best regards Ronnie

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7/13/2018 8:59 AM	Rate (0)
Willybong Silver Member Joined: 2/11/2015 Last visit: 1/21/2026 Posts: 516 Rating: (36)	Hi Roverman, Maybe that's not help you but, If You not want to modify the FC... Try to do like #dP says, create a DB with DINT elements and pass there the REAL hours value, and, on the HMI ask for the elements of DB. Trying to help you,

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This contribution was helpful to 1 thankful Users #dP

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