Controls, Indicators, and Displays
SORVALL
®
Centrifuges
3-6
NOTE When changing mode, rpm/RCF values may appear a
digit or two off from the original set value. The centrifuge
translates set RCF values to rpm whole numbers for
speed control purposes, then calculates that rpm whole
number to the closest RCF value. There is no cause for
concern; speed control accuracy is not compromised,
and the slight value difference will not affect the run.
The run duration (from start to termination, when deceleration
begins) setting or control method is changed by pressing one of the
three grouped Primary Function keys:
• TIME is pressed to specify a length of time (minutes and seconds,
to a maximum of 99:99) from run start to termination. In the RUN
display, minutes and seconds begin counting down from the input
value when START is pressed. The run terminates and deceleration
begins when the timer reaches zero.
• HOLD is pressed to specify a continuous run which, once started,
runs until STOP is pressed (terminating the run and initiating
deceleration). During a continuous run, HOLD will be in the SET
display, and the time elapsed from when START was pressed will
appear in the RUN display. The timer will accumulate up to 300
minutes – if a run continues beyond that, displayed run time will no
longer reflect elapsed time, but will remain fixed at 300:00. Whenever
it is possible for such an extended run to occur, an external timing
method is recommended.
• ACE is pressed to specify an Accumulated Centrifugal Effect™
value. When ACE control is selected, the centrifuge calculates the
effect of speed in relation to time (the shaded area in the illustration
at left), adjusting run duration to account for acceleration variation.
This variation can be attributed to rotor load/configuration differences
(affecting inertia), fluctuations in line voltage (affecting motor
power), or slight mechanical differences including normal wear.
When START is pressed, the realized ACE value begins to accumulate
in the RUN display. The run will terminate and deceleration will
begin when the specified ACE value (expressed as ∫ω
2
dt*,
controllable up to 9.99 x 10
30
[displayed as 9.99e30]) is reached.
After termination, the RUN display will continue to accumulate
until the rotor stops – this run total is for reference; care should be
taken not to confuse the RUN display's final accumulation with the
controlling input/timeout value, found in the SET display. Compared
to control by time, ACE selection provides a more advanced and
relevant form of run duration control, thereby improving separation
consistency, run reproducibility, and dependability of results.
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TIME
SPEED
RUN
TOTAL
TERMINATION
SET POINT
Accumulated Centrifugal Effect™
calculating the area under the curve
* The integral value can be calculated deriving the following formula:
∫w
2
dt = w
2
∫dt = ω
2
∆t
Where: ∆t = Change in time (seconds)
and ω
2
= Angular speed
= 2π [n/60]
n = Speed (rpm)
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