Digital Control for Analog Mux
A single Voltmeter or Digital Panel Meter DPM can monitor 8 Analog inputs from sensors or potentiometers using a Mux chip and creating simple digital controls for that. Four pushbuttons on the front panel control the scanner. One 4051 is used to multiplex 8 trimpots that hold the Analog Alarm Settings. The channel number in BCD is translated to a LED channel Display with a 4511 chip.
Timer and Counter Module
A digital counter monitors the number of times a process goes beyond a certain temperature limit over a long cycle of time. This circuit has a Analog Timer and Digital Counter. The Analog timer turns on an Alarm if the Temperature Limit transition is very long. U1 CD4541 is a Timer with Long Duration Ability. This timer is started by a low pulse from earlier circuit, when the temperature goes above setpoint, a low state is at U2A inputs, this starts the timer.
Pt-100 RTD Four Point Alarm
Four points in a Closed Loop Temperature Control System is Monitored and a Alarm set to go off when the temperature goes beyond the set limit. Here 4052 is used as an analog multiplexer, U3A TL062 opamp is wired as a 1mA Constant Current Source. It pumps 1mA into U2 4052 pin 13 X . Depending on BCD code on inputs A, B of 4052.
Sample and Hold with CD4066
A sample and hold is like an analog memory. If The digital control A is low 4066 switch is open, and when A is high switch is closed. U2B is a buffer so as to ensure quick charging of C1 thru 4066 on resistance of 100E. U2A is a FET input opamp buffer which does not load or drain the cap C1.
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