options . . utilities . . calibration ........................................................................................................... ALARM LIMITS display
The Alarm Limits & Shutdown interval display is shown in Figure 862.0Note that even though this display overwrites the
entire Main Operating Display, the plant operation and data gathering continues uninterrupted.
This display shows the current process deviations that are allowed before alarms are annunciated. Also shown are the
time intervals during which a continuous alarm must persist before automatically causing the process to be halted. If any
time interval is set to 0 seconds, that particular alarm is disabled, will never annunciate, and can never shut down the
process. The maximum shutdown interval is 255 seconds.
The alarm limit for either the virgin or recycle scale is shown in per cent of total aggregate request. Deviations of plus or
minus the limit shown are allowed. For example, at a target aggregate rate of 200 dTPH and 20% recycle, a 5% recycle
scale error would be annunciated if the actual recycle rate was 30 TPH (15% of 200 TPH) or 50 TPH (25% of 200 TPH).
The alarm limit for A/C Blend is the difference between the target A/C value in percent and the actual measured A/C value
in per cent. Again, the allowable deviation is plus or minus the percentage shown. For example, at 200 TPH of virgin
aggregate a target of 5%mA/C requires 10.5 TPH of A/C. At 9.9 TPH the added A/C is 4.7x and the deviation is -
0.3%mA/C. At 11.2 TPH, the added A/C is 5.3x and the deviation is +0.3%mA/C.
The Divert Error does not need a limit value. It is the time during which the RUN-DIVERT valve is not in the expected
The Feeder Error also does not need a limit value. It is the time during which the low aggregate alarm switch or some
other means indicates that inaccurate delivery of aggregate is probably occurring.
The Continuations Options are:
Return to the previous display.
Gain access to the data shown so that one or more of
the parameters can be changed. Access cannot be
obtained if the DATA KEY is in the DATA LOCKED
Print this screen display. The printer must be
turned ON and SELECTed.
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SYSTEMS Equipment Corp. 8/31/89 Page (30)