Prescaler output option – Red Lion C48C User Manual
Page 42
PRESCALER OUTPUT OPTION
The prescaler output is useful for providing a lower frequency scaled pulse
train to a PLC or another external totalizing counter. The prescaler output
provides programming parameters to determine when to turn the output on
(
PScOAt
)[display dependent] and when to turn the output off (
PScLEn
) [input
pulse dependent].
The prescaler output turns on when the LSD (least significant digit) of the
display value changes by one digit (
1 dig
), or when the 2nd LSD changes by
one digit, effectively a display change of 10 (
10 dig
).
The (
PScLEn
) is the turnoff point of the prescaler output after the
programmed number of positive edge input pulses (1 through 9).
Note: The activation of the prescaler output is dependent on the display value
change. The deactivation of the prescaler output is dependent on the positive
edge of the input pulse, and NOT display value change.
During manual reset of the counter, an activated prescaler output is reset
(turned off).
The optimum prescaler length value for a specific prescaler value and
prescaler output at (
PScOAt
) setting can be obtained from the tables at right.
Where possible, the optimum value will provide a duty cycle close to 50%.
When
PScLEn
value is obtained from the tables:
Effective Prescaler Output Frequency = Application’s Max. Input Frequency
2
×
(
PScLEn
- 0.5)
As a rule, the counter connected to the prescaler output should be able to
accept a count rate at or higher than the “Effective Prescaler Output Frequency”.
-36-
Example: A manufacturer needs to measure the flow of a liquid to their
process in tenths of a gallon. They also require a signal to their PLC to
register the total number of gallons used. The flow meter outputs 50 pulses
per gallon. Using the programming parameters set as described at right, the
prescaler output provides one output pulse for every 50 input signal pulses,
or 1.0 display value change.
PScALr
=
0.20000
(Display will change 0.1 gallons for every 5 input
signal pulses)
PScOAt
=
10dig
(Prescaler output will turn on as the 2nd LSD changes
by one digit, or when the display changes to every
whole gallon.)
PScLEn
=
9
(Prescaler output turns off 9 input pulses after turn on.
Effectively 0.2 gallons after each whole gallon.)
For
P
PS
Sc
cO
OA
At
t
=
1
1 d
di
ig
g
0.50001-1.00000
1
0.25001-0.50000
2
0.17001-0.25000
3
0.12501-0.17000
4
0.10001-0.12500
5
0.08251-0.10000
6
0.07001-0.08250
7
0.06251-0.07000
8
0.00001-0.06250
9
PRESCALER
VALUE
P
PS
Sc
cA
AL
Lr
r
OUTPUT LENGTH
VALUE
P
PS
Sc
cL
LE
En
n
9
0.00001-0.62500
8
0.62501-0.70000
7
0.70001-0.82500
6
0.82501-1.00000
OUTPUT LENGTH
VALUE
P
PS
Sc
cL
LE
En
n
PRESCALER
VALUE
P
PS
Sc
cA
AL
Lr
r
For
P
PS
Sc
cO
OA
At
t
=
1
10
0 d
di
ig
g