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MODEL 3081 pH/ORP SECTION 2.0
INSTALLATION
2.5 POWER SUPPLY/CURRENT LOOP
2.5.1 Power Supply and Load Requirements.
Refer to Figure 2-6.
The minimum power supply voltage is 12.5 Vdc and
the maximum is 42.4 Vdc. The top line on the graph
gives the voltage required to maintain at least 12.5
Vdc at the transmitter terminals when the output sig-
nal is 22 mA. The lower line is the supply voltage
required to maintain a 30 Vdc terminal voltage when
the output signal is 22 mA.
The power supply must provide a surge current
during the first 80 milliseconds of start-up. For a
24 Vdc power supply and a 250 ohm load resistor
the surge current is 40 mA. For all other supply
voltage and resistance combinations the surge
current is not expected to exceed 70 mA.
For digital (HART or AMS) communications, the
load must be at least 250 ohms. To supply the 12.5
Vdc lift off voltage at the transmitter, the power sup-
ply voltage must be at least 18 Vdc.
For intrinsically safe operation the supply voltage should not exceed 42.4 Vdc.
FIGURE 2-6. Load/Power Supply Requirements
FIGURE 2-7. Power Supply/Current Loop Wiring
2.5.2 Power Supply-Current Loop
Wiring. Refer to Figure 2-7.
Run the power/signal wiring through
the opening nearest terminals 15 and
16. Use shielded cable and ground the
shield at the power supply. To ground
the transmitter, attach the shield to the
grounding screw on the inside of the
transmitter case. A third wire can also
be used to connect the transmitter
case to earth ground.
NOTE
For optimum EMI/RFI
immunity, the power sup-
ply/output cable should
be shielded and
enclosed in an earth-
grounded metal conduit.
Do not run power supply/signal wiring
in the same conduit or cable tray with
AC power lines or with relay actuated
signal cables. Keep power supply/ sig-
nal wiring at least 6 ft (2 m) away from
heavy electrical equipment.
An additional 0-1 mA current loop is
available between TB-14 and TB-15. A
1 mA current in this loop signifies a
sensor fault. See Figure 4-3 for wiring
instructions. See Section 8.3 or 10.3
and Section 12.0 for more information
about sensor faults.
DWG. NO. REV.
40308122 B