Hoffer Flow Controls CAT3-DC-MIL User Manual page 23

current
Where:
AF = Is the 20mA maximum Flow rate value.
If the calculated flowrate is greater than the AF setting, the
current will be set to 24mA to indicate an "Over-range" condition.
After calculating the current, the Microcontroller digitally sends
the current information to the Loop Driver. The loop driver,
located on PCA183, uses the digital information sent to it by the
Microcontroller to set the current of the loop. The Loop Driver
also supplies power to the Microcontroller.
The analog output response time to reach steady state due to a
change in the flow rate is approximately 1/8 of a second. When
flow stops, the time for the analog output to return to 4 mA will
be between .25 and 8 seconds, depending on the Maximum
Sample Time (MST) setting. MST is adjusted using the NB=
(DATA) command, where NB is a value between 1 and 80. The
default MST setting is NB= 1.
recommended for low flow applications where the minimum input
frequency is below 1 Hz.
5-5 Wiring
When installing CAT3-DC-MIL, it is a good practice to use shielded
cables for all input and output signals. The shield should be connected
to the earth ground lug on the CAT3-DC-MIL. The shield on the
opposite end of the cable should be left open.
This wiring practice is mandatory in order to comply with the
requirements for Electromagnetic Compatibility, as per EMC-Directive
89/336/EEC of the Council of European Community.
5-6 Flowmeter Installation and Initial Startup
The performance of the turbine flowmeter is affected by the fluid swirl
and non-uniform velocity profiles. It is advisable not to locate the
meter run immediately downstream of pumps, partially opened valves,
bends or other similar piping configurations. In addition, the area
surrounding the flowmeter should be free of sources of electrical noise
such as motors, solenoids, transformers and power lines which may be
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4 mA 16 mAx
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Installation
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flowrate
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AF
Adjusting the MST is only
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