7-2
MODEL 54 C
SECTION 7
THEORY OF OPERATION
OUTPUT LOGIC.
The behavior of the Model 54 ana-
lyzer's outputs and relays are determined by various
states called 'modes'.
The modes are:
1. Fault mode
- fault conditions cause this mode to turn
on.
2. Timer mode - the interval timer causes this mode to turn
on.
3. Hold mode
- user switches this mode on and off.
4. Simulation
- user switches this mode on by simulating
output(s).
Normally the analyzer's relays and outputs track the
process.
The fault mode sets the outputs and relays to their pre-
set programed fault values (
Hold mode overrides timer state. If hold is activated,
timer continues count to time out, but does not change
state until hold is removed. The relays always open in
hold mode (Note that Relay 4 may be wired normally
closed as the relay is open when the LED is on). The
timer mode initiates the hold mode for all relays except
the timer relay. The simulation mode affects only the out-
put(s) being simulated. (one at a time).
Fault mode overrides normal operation.
Timer mode overrides fault mode.
Hold mode overrides Timer and Fault modes.
Simulation mode overrides hold mode for the
output(s) simulated.
If the hold “Enable feature” is selected then Hold
mode can be accessed via the calibration menu.
When hold mode is on, the display timeout is disabled
until hold mode has been turned off. If the Hold “20
min timeout” is selected and hold is on then display
timeout and security lockout are disabled for 20 min-
utes after the last keypress. At the end of this 20
minute period Hold mode automatically turns off and
the display times out.
Normally the display defaults to the operating display
after two minutes of no keypresses. If output is being
simulated, 2-pt buffer calibration is performed or if “20
min timeout” and Hold mode is on, then the display
times out after 20 minutes.
If a security code is entered, the security will lock
when the display times out.
INTERVAL TIMER.
The interval timer may be used for
periodic sensor cleaning, or process adjustment.
The interval timer settings are:
1. Switch
- Enables or disables the interval timer.
2. Interval
- the time period between cycles.
3. Repeats
- the number of relay activations per cycle.
4. On time
- the time period of one relay activation.
5. Off time
- the time period between two or more relay
activations.
6. Recovery - the time period following the final relay acti-
vation.
The cycle begins at the Interval time when the Switch
is turned on. When the Interval time has expired the
analyzer activates Hold mode and relay 3 is activated
for the On time period. If the number of Repeats is
greater than one, the relay is deactivated for the Off
time period and reactivated for the On time period
until the number of relay activations equals the num-
ber of Repeats selected. When the final relay activa-
tion is complete the relay is deactivated for the
Recovery time period. Note that no Off time period fol-
lows this last relay activation. When the Recovery time
period expires the Hold mode deactivates and the
cycle repeats, beginning with the Interval time.
Typically, the interval timer is configured with a long
Interval, several Repeats of fairly short On times, fairly
short Off times and a Recovery time which allows the
process to stabilize. Setting Interval to zero results in
continuous pulsing and setting Off time to zero will
cause a single pulse equal to [On time x Repeats].
Note that the hold mode supercedes the Timer State.
If the hold mode is on, the present interval time con-
tinues to expire and once expired the interval timer is
suspended until hold state is removed.
Summary of Contents for 54C
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