SCALING FOR RATE INDICATION
Scaling the Rate channel involves programming the CUB5 so that input
pulses to the unit are scaled to the desired display units.
Note: It is not necessary to increase the pulse information to obtain higher
resolution.
The operator keys-in a display value and a corresponding rate value. The
location of the scaling point should be near the process end limit for the best
possible accuracy. Once these values are programmed, the indicator calculates
the slope of the rate display automatically and scaling is complete after decimal
point selection. Input frequency can be read directly if rate display and rate
input values are programmed to “1” and “1.0”.
Note: The rate display will flash “r OLOLOL” if the display exceeds 999,999,
which means the unit must be re-scaled.
If the rate application is to display a specific display unit, it is only necessary
to know the number of pulses per desired display unit/s (feet, revolutions, etc.)
and in the desired time format, per second (1), per minute (60), or per hour
(3600) to scale the rate display. Use the following formula to calculate the rate
input value:
rAtE INP (Hz) = rAtE dSP x
pulses per unit
desired time format
WHERE:
rAtE INP = Rate input value.
rAtE dSP = Desired rate display value.
Pulses per unit = Number of actual input pulses.
Desired time format = 1 if rAtE dSP is to display units per second. 60 if
rAtE dSP is to display units per minute. 3600 if rAtE
dSP is to display units per hour.
EXAMPLE: Display is to indicate 1575 revolutions per minute (RPM). Input
pulses are 39 pulses per revolution.
rAtE INP (Hz) = 1575 RPM x
39 PPR
60
rAtE INP (Hz) = 1023.75
Since the rate input value can only be programmed in tenths, the value is re-
calculated by increasing the rate display value by a factor of ten. The display
value is continually increased until one of the following is reached.
1. The rAtE INP value’s least significant digit is no smaller than a tenth.
2. The rAtE dSP value exceeds 999,999.
3. The rAtE INP value exceeds 99999.9.
Note: For two and three, use the value that was calculated prior to exceeding
that value.
rAtE INP (Hz) = 15750 RPM x
39 PPR
60
rAtE INP (Hz) = 10237.5
15750 is entered for the rAtE dSP.
10237.5 is entered for the rAtE INP.
RATE
The rate value calculation uses the time measured between the first and last
pulse as the measurement period. The measurement period begins when a
negative going edge is received at the signal input A. When the Low Update
time has expired, the unit will end the measurement period on the next negative
going edge and update the display. The unit will count the number of pulses that
occurred during the measurement period and update the display, according to
the scaling value, at the end of the measurement period. To assist in stabilizing
an erratic display, increase Lo-Udt (Low Update Time) for a display averaging
effect. If the unit does not receive a negative edge within the period between the
low update and high update time, the unit will end the measurement period and
the input (rate) display will go to zero. At very low count rates, the update time
(measurement period) will be the actual period of one count cycle.
EMC INSTALLATION GUIDELINES
Although this unit is designed with a high degree of immunity to
ElectroMagnetic Interference (EMI), proper installation and wiring methods
must be followed to ensure compatibility in each application. The type of the
electrical noise, source or coupling method into the unit may be different for
various installations.
In extremely high EMI environments, additional measures may be needed.
The unit becomes more immune to EMI with fewer I/O connections. Cable
length, routing and shield termination are very important and can mean the
difference between a successful installation or a troublesome installation.
Listed below are some additional EMC guidelines for successful installation
in an industrial environment.
1. Use shielded (screened) cables for all Signal and Control inputs. The shield
(screen) pigtail connection should be made as short as possible. The
connection point for the shield depends somewhat upon the application.
Listed below are the recommended methods of connecting the shield, in order
of their effectiveness.
a. Connect the shield only at the panel where the unit is mounted to earth
ground (protective earth).
b. Connect the shield to earth ground at both ends of the cable, usually when
the noise source frequency is above 1 MHz.
c. Connect the shield to common of the unit and leave the other end of the
shield unconnected and insulated from earth ground.
2. Never run Signal or Control cables in the same conduit or raceway with AC
power lines, conductors feeding motors, solenoids, SCR controls, and
heaters, etc. The cables should be run in metal conduit that is properly
grounded. This is especially useful in applications where cable runs are long
and portable two-way radios are used in close proximity or if the installation
is near a commercial radio transmitter.
3. Signal or Control cables within an enclosure should be routed as far away as
possible from contactors, control relays, transformers, and other noisy
components.
4. In extremely high EMI environments, the use of external EMI suppression
devices, such as ferrite suppression cores, is effective. Install them on Signal
and Control cables as close to the unit as possible. Loop the cable through the
core several times or use multiple cores on each cable for additional
protection. Install line filters on the power input cable to the unit to suppress
power line interference. Install them near the power entry point of the
enclosure. The following EMI suppression devices (or equivalent) are
recommended:
Ferrite Suppression Cores for signal and control cables:
Fair-Rite # 0443167251 (RLC #FCOR0000)
TDK # ZCAT3035-1330A
Steward #28B2029-0A0
Line Filters for input power cables:
Schaffner # FN610-1/07 (RLC #LFIL0000)
Schaffner # FN670-1.8/07
Corcom #1VR3
Note: Reference manufacturer’s instructions when installing a line filter.
5. Long cable runs are more susceptible to EMI pickup than short cable runs.
Therefore, keep cable runs as short as possible.
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