Instruction manual

17
MODEL XMT-P pH/ORP SECTION 3.0
WIRING
3.1 POWER SUPPLY/CURRENT LOOP —
MODEL XMT-P-HT
3.1.1 Power Supply and Load Requirements.
Refer to Figure 3-1.
The supply voltage must be at least 12.0 Vdc at the transmitter ter-
minals. The power supply must be able to cover the voltage drop on
the cable as well as the load resistor (250 Ω minimum) required for
HART communications. The maximum power supply voltage is
42.0 Vdc. For intrinsically safe installations, the maximum power
supply voltage is 30.0 Vdc. The graph shows load and power sup-
ply requirements. The upper line is the power supply voltage need-
ed to provide 12 Vdc at the transmitter terminals for a 22 mA cur-
rent. The lower line is the power supply voltage needed to provide
30 Vdc for a 22 mA current.
The power supply must provide a surge current during the first 80 milliseconds of startup. The maximum current is about
24 mA.
For digital communications, the load must be at least 250 ohms. To supply the 12.0 Vdc lift off voltage at the transmitter,
the power supply voltage must be at least 17.5 Vdc.
FIGURE 3-1. Load/Power Supply Requirements
FIGURE3-2. Power Supply/Current Loop Wiring
3.1.2 Power Supply-Current Loop
Wiring.
Refer to Figure 3-2.
Run the power/signal wiring through
the opening nearest TB-2.
For optimum EMI/RFI protection . . .
1. Use shielded power/signal cable
and ground the shield at the
power supply.
2. Use a metal cable gland and be
sure the shield makes good elec-
trical contact with the gland.
3. Use the metal backing plate (see
Figure 2-6) when attaching the
gland to transmitter enclosure.
The power/signal cable can also be
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/signal wiring at least
6 ft (2 m) away from heavy electrical
equipment.
SECTION 3.0
WIRING