Red Lion LEGEND - Manual (Page 57)

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APPENDIX “C” - APPLICATIONS (Cont’d)
TYPICAL COUNTER/RATE APPLICATION
COAL FEED RATE & USAGE INDICATION
An industrial plant has an in-house coal fired boiler
that provides heating and powers an electric generator
used for secondary power. An auger feeds the coal into
the boiler furnace. The actual pressure of the boiler is
controlled by the feed rate of the auger. An indication is
required when the feed rate falls below or exceeds the
desired RPM levels. The plant manager also wants an
indication of the amount of coal that is used. The desired
auger revolution rate is between 25 and 35 RPM. A shaft
rotation speed of 30 RPM is equal to a feed rate of 1.8
tons of coal per hour. Rate and usage indication is to be in
10ths of tons per hour.
An PSAC can be used to sense a bolt head located on
the auger shaft. The count with direction x1 (CT =
DIRx1) is programmed in the program counter module
with input B left open to the unit counts in a positive
direction. The reset action mode is set to reset to zero and
the automatic reset is disabled. First the scaling required
for the counter is calculated.
The number of pulses must be calculated:
Number of pulses = # of rev x pulses per rev =
1 x 30 = 30 pulses/min (PPM)
Per hour = x time = 30 x 60 = 1800 PPH
The total scaling factor is calculated by the following
formula:
K
T
= Desired display units ¸ number of pulses =
18 ¸ 1800 = 0.01
The Count Scale Factor (SF) is calculated using the
following formula and the scale multiplier is chosen using
the general rule (reference scaling for count indication):
SF = K
T
¸ SCM = 0.01 ¸ 0.1 = 0.1
The decimal point location for the count
display is programmed for 0.0.
At 30 RPM the pulse rate per minute is the same
since a single bolthead is being sensed once each
revolution. Since it takes one hour at 30 RPM to
u s e 1 . 8 t o n s o f c o a l , t h e n u mb e r o f p u l s e s
accumulated in that hour will be 1800 (30 PPM x
60 min/hr = 1800). The Scale Factor needed is
0.01 (SF = desired reading/# of pulses = 18/1800
= 0.01). The rate display is to indicate RPMs with
a resolution in tenths, The total scaling factor is
calculated by the following formula:
K T = Desired display units ¸ number of pulses =
300 RPM ¸ 30 = 10
The Rate Scale Factor (SF) is calculated using
the following formula and the scale mutiplier is
chosen using the general rule (reference scaling
for count indication):
SF = K T
¸ SCM = 10 ¸ 10 = 1
It is then only necessary to program the Rate
Conversion Factor for Rate per Minute. Since the
application requires two presets for the upper and
lower limits, the outputs are programmed to the
Rate display. Both outputs are programmed for
boundary operation and output 1 is programmed
for “-” phase. The relay outputs are connected to
overspeed and underspeed indicator lights.