(a) Log Count-Rate Meter. The LCRM has a count-rate circuit for control and readout, it will also have period and level circuits that must be calibrated periodically to ensure proper alignment of the unit

The counting circuits can be checked by using a built-in oscillator to provide pulses at two or more repetition rates to the discriminator output The frequency of the oscillator can be verified by using scaler output and a scaler The meters and recorders can then be calibrated

The period circuits can be calibrated from a built in ramp generator The ramp generator provides signals that increase linearly with time and at various rates The signal is applied to the operational amplifier that feeds the differen­tiator The period circuit differentiates this signal and provides a constant period indication for calibration of the readout circuits This also provides a means for setting the period trip level.

(b) Channel Checkout. Some means should be pro­vided at the preamplifier input for checking and calibrating the complete channel Ideally, a neutron source inserted near the neutron sensor would provide complete system checkout. Since this is generally not possible, the system is checked from the preamplifier A calibrated pulser provides the input signal to the preamplifier, and meter, recorder, and scaler readings are verified Level and period trips are also verified

5- 2.8 Control and Safety Circuits[14]

A start-up channel system is shown in Fig 5 15 The system consists of independent channels for control and local indication but with a common recorder for switch selection of a desired readout channel. The three channels provide the redundancy necessary to satisfy safe operation of the reactor and also provide for sufficient channels so that loss of a single instrument need not result in lost reactor operating time. The shutdown circuits associated with the three channels are arranged in a two-out-of-three shutdown logic, i. e., two instruments must trip before scram is initiated. The initiating shutdown circuit is shown in Fig 5.15