A block diagram of a logarithmic amplifier (log N) is shown in Fig. 5.17. The log N amplifier has two essential circuits for signal conditioning. The first is the log section, which converts the detector signal to a logarithmic output The second circuit is the period differentiator circuit

The input signal is biased to range over nine decades. So that this signal can be continuously monitored, it is converted to a log signal in the log amplifier circuit The circuit consists of an operational amplifier with an active feedback element, namely, the grounded-base transistor. The circuit can be described by the following equation

e = Eg log ~- (5 3)

lo

where e = output voltage

E0 = offset voltage of the operational amplifier і = input current from the CIC I0 = offset current of the operational amplifier

The output voltage then changes by a factor of 9 for an input current change of nine decades

The log N amplifier circuit is followed by an amplifier that conditions the signal for the meter and recorder outputs and provides a signal for the period differentiator.

The operation of the period differentiator circuit is the same as that for the circuit described in Sec 5-2.4(c) The output of the period differentiator circuit drives a meter and recorder and provides a signal for the period trip circuit. The period trip circuit alarms when the preset time value is exceeded. The trip circuit is described in Sec 5-2.4(e).

5- 3.5 Calibration and Checkout

The log N amplifier shown in Fig 5.17 has two built-in calibrators for checking out the system. The first is a current source with several fixed ranges used to calibrate the log N circuits, meters, and recorder. The second calibration device is a ramp generator for checking the period-differentiator circuit, meter trip, set point, and recorder The period calibrator is described in Sec 5-2 7 These two calibrators provide a means for checking the entire system.

5- 3.6 Control and Safety Circuits

The log N period amplifier provides an alarm (trip) when the period exceeds the set-point value The trip module and shutdown circuit are described in Sec. 5-2 8.

I CONTROL I NUCLEAR PANEL—- 4*—C0NS0LE “Л

INSTRUMENT I CONTROL CENTER NO 2——— *4*——- CABLE ROUTING ROOM

LEGEND A TO ANNUNCIATOR, CONTROL CONSOLE В TO ANNUNCIATOR, NUCLEAR PANEL 1 RELAY TRIP, OPERATING SHUTDOWN CIRCUIT (FLUX LEVEL, HIGH) 2 RELAY TRIP, OPERATING SHUTDOWN CIRCUIT (ION-CHAMBER VOLTAGE LOW)

Fig. 5.18—Block diagram of high-flux channels 9, 10, and 11