Apart from the DA163 quad amplifier module, the IN163 dual integrator module is the most complex module of the whole Hitachi 240 analog computer. It contains the necessary electronics for two high precision integrators, each of which requires an operational amplifier from a DA163 module to work in a computing setup.

The idea of analog integration in electronic analog computers is to use a (precision) capacitor in the feedback loop of a very high gain operational amplifier. For practical applications this feedback capacitor should be selectable for its capacity to allow different time scales for integration.

Apart from this there has to be a way to charge the capacitor to a given value prior to a calculation to implement initial conditions.

Most of these switching operations are implemented in electronic form in the Hitachi 240 analog computer (only the time scale selection is accomplished by bottle plugs plugged into the removable analog patch panel of the machine).

The picture on the right shows the board containing the necessary electronics to perform these switching operations. The electronic switch used here is the same as the one used as the chopper switch in the DA163 quad amplifier.

On the right of the picture the input networks can be seen - the high precision resistors are frequency compensated by small capacitors soldered in parallel over them.

Behind the patch panel

The heart of the IN163 dual integrator is shown on the picture on the left - the integrating capacitors. These capacitors are not only very (very!) expensive but also very accurate with a very low temperature coefficient. When servicing units like these make sure to clean all soldering joints with some alcohol to remove even the slightest remains of sweat, etc. since even the remains of touching these circuits with the bare hands may introduce non-negligible errors in a calculation.