Feature
OPEN PROTOCOL
Miniaturisation and increased processor speeds allow for compact programmable open protocol controllers with user interfaces included .
COMMON DATA
STEP 5 STEP 7 STEP 4 STEP 6
Massive increase in processing capability linked to IP Ethernet becoming the international standard . Controllers include webserver ( Graphics )
Industry bodies ( ASHRAE ) and companies ( Echelon ) designed open protocols for adoption by industry . Due to cost adopted on RS485 low order networks .
Reduction in price of Ethernet and rapid adoption of IP leads to combining data from low order networks to IP through gateways . i4 Group / iLED temperature , pressure , or humidity at a particular value . Digital devices measure and control an open / closed , or on / off status .
In an example of determining the capacity of the controller required , one would need to evaluate the plant system . You may have two temperature sensors , two valves , a heater bank that is either on or off , a fan , a pressure switch , and a static supply pressure . Simply taking the input / output ( I / O ), one would partner a controller that has a minimum of the I / O that are required to be controlled . Typically , it is also common practice to accommodate spare I / Os . A consultant would specify that there must be a 10 or 15 % spare capacity included , so that sensors can be added for future expansion . For the IT orientated individuals , controllers can be likened to a network switch where all the endpoint devices are tallied that need to be connected , and the same principle of sizing is applied .
CONTROLLER PROGRAMMING Who does the controller programming ? Well , this is in fact a very good question and I believe one worth getting your input on !
There is an assumption from various perspectives that when for example an air handling unit arrives on site , it will already
www . hvacronline . co . za RACA Journal I September 2021 31