Question: In the fluid filling operation of Example, suppose a sensor (e.g.,a submerged float switch) is used to determine whether the contents of the tank have been evacuated, rather than rely on timer T2 to empty the tank

(a) Construct the ladder logic diagram for this revised sys-tem.

(b) Write the low-level language statements for the system using the PLC instruction set in Table.

TABLE 8.11 Typical low-Leval Language Instruction Set for a PLC

STR           Store a new input and start a new rung of the ladder.

AND           Logical AND referenced with the previously entered element. This is interpreted as a series circuit relative to the previously entered                   element.

OR             Logical OR referenced witn the previously entered element. This is interpreted as a parallel circuit relative to the                         previously entered element.

NOT           Logical NOT or inverse of entered element.

OUT          Output element tor the rung of the ladder diagram.

TMR Omer element. Requires one input signal to initiate timing sequence. Output

is delayed relative to input by a duration specified by the programmer In seconds. Resetting the timer is accomplisbed by interrupting (stopping) the input signal.

CTR Counter element. Requirne two inputs! One is the incoming pulse train that is counted by the CTR element, the other is the reset signal indicating a restart of the counting procedure.

Example: Consider the fluid storage lank illustrated in Figure. When the start button X1 is depressed, this energizes the control relay C1. ln turn, this energizes solenoid 51, which opens a valve allowing fluid to flow into the tank.