A 1756-OF8 is a 0…20 mA module, and at full counts it puts out 21.29 mA. Nothing in the hardware knows that the positioner on the end of the wire wants 4 mA for closed and 20 mA for open, or that 0 mA on an air-to-open valve is the same as closed and 21 … Read more
A 1756-IF8 analog input in integer mode lands on roughly -20,030 counts at 4 mA and 30,920 at 20 mA, which are not numbers anybody memorises. If the value in front of you is 3277, the card in the rack is a 1769-IF4 or 1769-IF8 running the Scaled-for-PID data format, and none of the 1756 … Read more
A Pt100 RTD input wired two-wire over 22 m of 0.5 mm² cable into channel 0 of a 1756-IR6I reads 104.1 °C in a bath that the reference thermometer says is 100.0 °C, and the same sensor with its third lead landed on RTN-0/C reads 100.0 °C. Lift lead A off the module and the … Read more
A DINT stops at 2147483647, and 27648 multiplied by 77673 is 2147503104. That is the whole of the problem with fixed-point scaling in STL: the arithmetic is exact right up to the statement where it is not, and *D reports the crossing by setting OV and OS rather than by refusing to run. Here is … Read more
On an S7-1500 a 4 to 20 mA channel reads 0 counts at 4 mA and 27648 counts at 20 mA, and a channel with wire-break diagnostics enabled reads 32767 when the loop opens. Those three numbers decide the rest of this page: what goes in the MIN and MAX pins of NORM_X, what SCALE_X … Read more
How to pick discrete and analog I/O, get sinking and sourcing right, set RPI and electronic keying, wire a 4-20 mA loop and scale the raw counts.
Wet well level control, pump alternation that shares the wear, chlorine dosing with long dead time, and remote sites over cellular Modbus that go quiet.
PLC Programming PID Control In the previous article, we gave information about what is PID and PID control. Now we will learn how to control the pressure with PID in PLC. PLC PID Control Automation In the following program example, the PID instruction is used to control the pressure of a vessel using a pressure … Read more
A closed-loop control system for position control is comprised of proportional integral and derivative circuits and is often referred to as a PID (proportional–integral–derivative controller ) PID control is a common closed-loop system used to maintain physical property such as pressure and temperature in automated processes. the PID instruction controls the closed-loop by comparing the … Read more