Chapter 1. Installation
14 DigitalFlow™ Multipurpose Ultrasonic Liquid Flowmeter Startup Guide (1- and 2-Channel)
1.7.8 Wiring an RTD Inputs Option Card
The Model DF868 can accommodate up to four RTD (Resistance Temperature Device) inputs option cards. Each RTD
inputs option card provides two direct RTD inputs (designated as A and B).
Each RTD input requires three wires, which should be fed through one of the conduit holes on the bottom of the
electronic console. (For maximum accuracy, the three wires must be of equal length.) Wire this terminal block in
accordance with the pin number assignments shown in Figure 10 on page 16.
1.7.9 Wiring a 0/4-20 mA Analog Outputs Option Card
The Model DF868 flowmeter can accommodate up to 4 analog outputs option cards. Each analog outputs option card
includes four isolated 0/4-20 mA outputs (designated as A, B, C and D).
Connections to these outputs may be made with standard twisted-pair wiring. The total current loop impedance for
these circuits must not exceed 1000 ohms. Wire this terminal block in accordance with the pin number assignments
shown in Figure 10 on page 16.
1.7.10 Wiring a MODBUS Option Card
A modified DF868 can use the RS485 standard for MODBUS communications. This standard allows up to 32 nodes
(drivers and receivers) on one multidrop network, at distances up to 4,000 ft (1,200 m). To connect the instrument(s) to
the host system, the factory recommends using a 24-gauge (24 AWG) twisted-pair cable with a characteristic
impedance of 120 ohms and a 120-ohm termination at each end of the communications line.
The MODBUS option card must be plugged into either slot 5 or slot 6 of the DF868. On the option card, pin 1 is the
[TMT-] inverting or negative connection and pin 2 is the [TMT+] non-inverting or positive connection. To link the DF868
to the control system, connect the two wires of the twisted-pair cable from these terminals to the corresponding
terminals at the control system, in accordance with the pin number assignments shown in Figure 10 on page 16.
Note: If two MODBUS option cards are installed in the DF868, only the card in slot 5 is activated.
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