3/18/2017 2:22 PM | |
Posts: 5 Rating: (0) |
Hello, I am trying to sort some existing code on site using FB41 CONT_C. FB41 is (incorrectly) called every 1ms causing comms issues. I need call at a more sensible interval and re-tune the PIDs. PV_IN input to FB41 is in engineering units litres/hour. This has been scaled from analogue input (integer) 0-27648 = 0 to 66,000 litres per hour. At the other end the PID output LMN seems to be scaled by a block which takes a range 0-100 and converts it to an integer for the analogue output. Is 0-100 chosen for this as it matches LMN_ LLM , LMN_HLM? I am seeking a better understanding of FB41 with regard to scaling of engineering units as follows: LMN = (output of LMNLIMIT) x LMN_FAC + LMN_OFF LMN_FAC has the default 1 and LMN_OFF the default 0 so by default LMN = output of LMNLIMIT My question is what exactly is "output of LMNLIMIT"? Is it (roughly) = (SP_INT - PV_IN) x Gain and scaling this between LMN_HLM - LMN_LLM? Or does LMN_HLM, LMN_LLM have nothing to do with scaling and just provide a value to drive QLMN_HLM, QLMN_LLM for monitoring purposes? My analog outputs are currently generated by taking LMN and scaling using 0-100 as a range to an integer 0-27648 for the analog output. I am unsure if 0-100 is correct or it should match the flow meter range of 0-66000 litres/hour. Probably not as this analogue output runs a pump 0-3000 rpm. -thank you for your time -Kurt ------------------------------------------------------------------------------------------ |
Last edited by: Min_Moderator at: 3/20/2017 10:24:56 AMNew subject after splitting |
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