Abstract
In order to satisfy the needs of large scale instrumentation for current industrial processes, an analog controller with capacitance memory circuit is developed.
In this controller, a part of operating circuit works as memory circuit for manual control. So, using a simple switching circuit, the transfer from an automatic operation to a manual operation and vice versa is performed bumpless without a balancing operation.
This memory circuit is also suitable as a pulse/analog converter, and it is simple to modify the controller as an output station of DDC system which possesses the function of a backup controller for computer failure.
Main component parts of this controller are operational amplifiers. A differential level shift circuit is designed to operate this circuit with a single 24V DC common power supply. This improves system reliability through battery backup against power failure.
To realize a stable capacitance memory circuit, a high input impedance operational amplifier is developed. This amplifier has N channel junction FET input stage and the source drain voltage of FET is kept constant regardless of the input voltage. The input bias current of the operational amplifier is less than 1.5pA (at 25°C). With this amplifier, the drift rate of memory circuit is less than 1% in 70 hours.
