Stephen Mitschke
August 12th, 2003, 12:38 PM
Hi All,1. - how many can PID be connected in a segment H1@31.25 Kbps??? 2, - how many blocks of functions as maximum it can exist in a segment H1??3. - which the maximum consumption of current of a segment H1 is??? greetings, FreddyPCE.[Verhappen, Ian] This is similar to an earlier thread, and once again theanswer will be - it depends. It depends on the how you DESIGN your segmentsand system, the components and host, and how fast you want everything to run(cycle time). Perhaps others on the list can provide some other informationas well.- - - - FreddyAs Ian mentioned, it depends on several factors, but may be this can helpyou to stablish a reference:1.- As PID is only a Function Block you can put several PID's in a H1segment it is not a limitations of electrical consumption but time, the morePID's executed in a segment more time will be consumed, so the performanceof the control may be slow.2.- New Fieldbus devices has instantiation capabilities, this feature allowuser decide what type of FB and quantity of each will be executed by afieldbus device, Smar devices can execute up to 20 FB's in a single device,the user decide wich FB's will be executed, some other manufacturers has noinstantiation capability yet on their devices, you need to check what typeof FB and quantity can be executed on each device.Again FB's don't consume energy but time, some FB's are executed locally ina Fieldbus Device where the output is not linked to other FB's in thesegment, then no time is consumed in the line, if the output of the FB islinked to another FB outside the device then time is consumed then you needto becareful.3.- Some field devices consume up to 12mA, you can have 12-16 devices in thesegment, devices with higher consumption will reduce the number of devicesin the line.Rick CastaņedaSmar Mexico-= - - - - - Hi IanIf I am not mistaken, some vendors (i.e. Honeywell) used to putarbitrary limits on the number of outputs their host can support on asegment. In effect, this tends to limit your PID count far more than allthe other conditions such as timing and power consumption. Is this stillthe case?RegardsEric Byres[Verhappen, Ian] What is limited, as I understand it, and it is not onlyHoneywell, is the limit on how many blocks can be handled per second. Thisis related to the bandwidth issue and as you suggest certainly needs to beverified for EVERY manufacturer you are considering as a host.- - - - - These are not arbitrary limits they are limits based on the availablebandwidth of a particular segment and the memory within the Fieldbus I/Oprocessor. All manufacturers have a limit, you need to look at VCRlimitations as well. RegardsRaj KhemchandaniFieldbus Knowledge ManagerHoneywell International