Fluke 875 Action of Green Safe/Reset Light and Alarm During ECS Test, Low Voltage Ramp Generator

Function Description

Readout Module876A-1 4

NOTE

During the ECS test, all alarms are muted; that is, their operation is disabled until the completion of the test. During this six-second period there is no warning of a high radiation condition. If this situation is not tolerable, two containment monitors must be installed.

Action of Green Safe/Reset Light and Alarm During ECS Test

The behavior of the green SAFE/RESET panel light during the test is as follows:

A pass condition is indicated by the green light remaining lighted throughout the test.

A fail condition is indicated if the green light goes out at the end of the test.

Circuit Actions at Manual and Automatic Initiation of ECS Test

Whether the ECS test is initiated automatically or at the will of the operator, a trigger signal is delivered to pin 4 (manual) or pin 5 (automatic) of U206, whose output initiates the low voltage ramp generation. Automatic operation may be disabled by the removal of jumper 200A. The system will then respond only to the pressing of the ECS button.

The circuit containing U201 (pins 5, 6, 7) and U208 (pins 11 and 12) constitutes a clock with a 0.976 millisecond repetition rate. It is followed by counters U204 and U205. The action of U204 is entirely restricted to automatic control of the ECS test, as is the output from pin 1 of U205 (note that it may be open-circuited by the removal of jumper 200A). However, the outputs from pins 3, 5, and 6 have functions that enter into both manual and automatic action. In addition, they involve both the ramp-generation and monitoring functions of the ECS board, and also enter into the operation of two important auxiliary functions: 1) generation of a muting pulse, so that the alarms will not be set off during the ECS test and;

2)re-initiation prevention--that is the prevention of malfunction on manual operation in case the operator inadvertently presses the ECS button more than once. The monitoring function is involved because the instant of generation of the latch-enable pulse occurs a precise time after the pressing of the ECS button initiates the test (toward the end of the test, when conditions have stabilized). The path from U205 pin 6 to the latch-enable generator may be seen to involve the following points: 1) pin 10, U203; 2) pin 5, U207 (input); 3) pin 6, U207 (output) and finally pin 11, U207, whose output drives the latch-enable generator Q205. The latch and latch enable functions will be explained with the monitoring circuits after the explanation of the ramp generation.

Low Voltage Ramp Generator

The elements that enter the generation of the low voltage ramp are U203, U208, U201, Q204, and associated capacitors, resistors, and diodes. U203 is an auxiliary element.

At the arrival of the trigger, Q204 serves the purpose of reducing the voltage previously at terminal 5 quickly to zero, at which instant the ramp-generator proper takes over. Basically, C210 is the charging capacitor, and the other components serve either as charging resistors or linear elements. Potentiometer R227, ramp voltage per second adjustment (RAMP V/SEC ADJUST), serves to determine the rate of charge of capacitor C210, and consequently, the rate of rise of the voltage applied to the detector plates.

The ramp that is generated by the ramp generator appears at terminal 5, where its maximum is only 6.2 volts. From terminal 5, it is connected to the high voltage generator on the power supply printed circuit board, where it controls the generation of the high voltage, as explained in the functional description of the power supply printed circuit board.

Monitoring Circuits of The ECS Board

The input to the monitoring circuits of the ECS board is on terminal 1, the output on terminal 8. The input on terminal 1 is effectively proportional to the current produced in the detector by the application of the

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