This is our simplest module, but it still has some interesting
features. It allows measurement and display of any of the signal lines on the
system backplane. The basic sensitivity of the meter is 1.999V full scale in
either polarity, but for signals with an absolute value of more than about 1.8V
an autoranging facility is activated, giving a tenfold reduced sensitivity of
19.99V full scale in either polarity. The meter decimal point is shifted so
that the voltage as displayed remains correct. The maximum voltage on any
signal line is always within this range, so the meter reading will always be
correct. However, if the measured voltage is more than about 12V in either
polarity, then the module that has produced the measured voltage is probably in
saturation. In general, signal levels should be kept below 10 volts, and
ideally in the 1-5 volt range.
The signal line to be measured is selected by a rotary switch and a two-position toggle switch. As explained elsewhere, all signal lines are arranged in pairs labelled (A) and (B), and the toggle switch selects which one of each pair is metered. The rotary switch has positions marked 1-8 for the eight pairs of filter output signal lines, and the next position is for the pair of signal lines which carries the outputs from the input modules, being labelled as (inputs). Note that there is an additional unlabelled position, which connects the meter to another pair of signal lines. These are not used at present, but are reserved for additional input modules that may be required for future applications. At the opposite end of the switch travel, next to the filter 1 position, is a position labelled (amp). This pair of signal lines is used to carry the outputs from one or two ratio amplifier modules, allowing them to be displayed on the meter.
In a normal system with one input module, most signals will be present on the A signal lines, so the toggle switch should be in the (A) (left) position to read these signals. However, when one or more gain/offset modules are used, the outputs from the individual stages in the module(s) will normally be available on the corresponding B signal lines, although other arrangements are also possible as described in the gain/offset module documentation. Therefore each filter signal can be measured and displayed both before and after offset correction, so the amount of offset on any signal can easily be ascertained at any time without disturbing the signal
