I've designed a system to simulate digital and anlogue inputs to a few PLCS.
Ive attached the schematic to aid in the understanding of the system
The digital inputs have been pretty simple to construct, using toggle switches connected to a 24 V common rail and thus switching on the respective input switch.
However, the analogue system have been giving me grief. The LCDs to display the current measurement uses 12 V DC to power the LCD panels, and the current measurement is being computed by 24 V DC, with a 10k ohm potentiometer and a 1.2k ohm resistor to keep the current at a maximum.
Theres been 4 sets of inputs (one for each RTU/PLC, 4 all together). These inputs are isolated.
One turns on fine with no voltage drop, however when I turn them all on, there seems to be a voltage drop across the entire system. I cant comprehend why, since our supply is 27.2 V, 5A and the entire input system should draw less than 1 A.
(LCDs use <15 mA and the current generation should <23mA) Theres 12 LCDs all together.
If someone could help me understand what is happening and what should be done to rectify the issue. Please let me know if I havent included enough detail with my question.
Ive attached the schematic to aid in the understanding of the system
The digital inputs have been pretty simple to construct, using toggle switches connected to a 24 V common rail and thus switching on the respective input switch.
However, the analogue system have been giving me grief. The LCDs to display the current measurement uses 12 V DC to power the LCD panels, and the current measurement is being computed by 24 V DC, with a 10k ohm potentiometer and a 1.2k ohm resistor to keep the current at a maximum.
Theres been 4 sets of inputs (one for each RTU/PLC, 4 all together). These inputs are isolated.
One turns on fine with no voltage drop, however when I turn them all on, there seems to be a voltage drop across the entire system. I cant comprehend why, since our supply is 27.2 V, 5A and the entire input system should draw less than 1 A.
(LCDs use <15 mA and the current generation should <23mA) Theres 12 LCDs all together.
If someone could help me understand what is happening and what should be done to rectify the issue. Please let me know if I havent included enough detail with my question.
