3 cautionary notes on communications, Toshiba – Toshiba LF600F User Manual
Page 139
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11.3 Cautionary Notes on Communications
Observe the following notes and limitations when you use the communications function.
■ Current output load
Load resistance:
Load capacitance:
Load inductance:
Cable length:
240 to 750 Q (including communications line resistance)
0.25 pF maximum (including communications line capacitance)
4mH maximum (including communications line inductance)
2 km
maximum (approximate value when 1.25 mm^ shielded
cable is used under standard operating conditions.)
Wiring cable
Use a shielded cable (CVV-S, etc) for wiring.
Interference on 4-20mA current signal
To communicate with the flowmeter, a digital signal (amplitude 0.4 to 0.8 V in the case of
500f2 load resistance) with a frequency of 1.2 to 2.2 kHz is superimposed on the 4-20mA
current signal. If a high-response receiving instrument is connected to the current output
line,
the superimposed communications signal may interfere with the instrument.
To
prevent this interference, put a
low-pass filter with a time constant of about 100 ms
into
the input circuit of the receiving instrument.
Current output
Figure 11.3 Filter connection example
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