ABB Functional Block Diagram Counter Blocks - CTU, CTD and CTUD

functional block diagram have up counter, down counter and up down counter blocks. up counter is an incremental counter, down counter is a decremented counter and up down counter perform both action when particular counter input bit is set. up counter and down counter have fixed input and output. and up down counter is combination of up and down counter inputs and output. operation of counter is same as ladder programming. each counter blocks assigned with a instance name. instance name is defined for counter blocks. for up counter instance name is CTU, down counter instance name is CTD and up down counter instance name is CTUD.

Up counter in functional block diagram

CTU is a up counter block in functional block diagram. up counter increment counter current value by 1 each rising edge of counter input. counter output is set to true when counter current value is equal to counter preset value. counter preset value and counter current value is word data type and integer value is allowed in counter preset value. below is the example of up counter in functional block diagram

in above example counter increment by 1 when counter input(CU) is set to true every rising edge. reset input reset counter current value to zero. output is true only when counter current value(CV) is equal to counter preset value(PV).when counter reset input is true and counter input(CD) is changed from false to true than counter value remains zero. counter increment value only when reset input is false and counter current value is less than counter preset value.

Down counter in functional block diagram

CTD is a down counter. each rising edge of down counter input decrement counter current value by 1 . counter load input load preset value to counter current value. when counter first initialize output is true because counter current value is equal to zero. set load input true to move counter preset value to counter current value.

above is the example of down counter in functional block diagram. when counter initialize at first time counter current value is zero and counter output is true if counter input(CD) is change from false to true than no decrement in counter current value. so for decrement counter current value load preset value to counter current value. once the load current value is set output is false, each rising edge of counter down input decrement counter current value. when counter current value reached to zero output is set to true.

UP DOWN counter in functional block diagram

CTUD is up down counter, it performs increment and decrement counter current value. up down counter perform increment operation when counter input load, reset and counter down(CD) are false and counter up rising edge detected. counter perform decrement operation when counter down rising edge detected and input of counter load, reset counter up is set to false.

above is the example of up down counter in abb plc. all inputs and outputs are combination of both up and down counter. Up down counter work as up counter if CD, load, reset is set to false and counter CU input is changed from false to true than counter increment value by 1. QU is output of up counter it set when counter (CV) is greater than counter preset value. up down counter operate as down counter when CU, RESET and load is false and preset value is set or counter current value is greater than zero. each rising edge decrement counter value by 1.QD is output of down counter it turned when counter current value is equal to zero.