Yokogawa EXA PH202 2-Wire pH/ORP Analyzer - Manual (Page 38)

IM 12B07D02-01E
Installation and wiring 3-5
3-3-3. Installation in: Hazardous Area-Non-Incendive
The EXA PH202S-N may be installed in a Category 3/ Zone 2/ Div.2 area without the use of safety barri-
ers. Maximum permissible supply voltage 31.5V
3-3-4. Liquid earth
In all circumstances, the sensor side of the measuring loop must be grounded to the measuring liquid.
The EXA PH202S uses advanced differential high impedance input circuits. This technique calls for a
grounding to the liquid. In addition to that the sensor checking circuits also use the liquid earth for meas-
urement of impedance of the sensors. All Yokogawa fittings have provisions for this connection. It is usu-
ally called liquid earth in all our manuals.
A separate connection should be made to the terminal numbered 14 in all cases to get a proper and sta-
ble measuring loop.
3-3-5. Access to terminal and cable entry
1. To access terminals remove the front cover of the EXA PH202S by releasing the 4 captive screws.
2. Thread the sensor cables into the connection space and connect the cables to the terminals as
indicated in the wiring diagram. Make sure all connections are firm and do not touch each other.
3. Screw the gland securely and tighten it to keep out moisture. DO NOT use a wrench to tighten the
nut.
4. The optional hose connection is used to guide the cables coming from an immersion fitting through a
protective plastic tubing to the transmitter.
3-4. Wiring of power supply
3-4-1. General precautions
Do not activate the power supply yet. First make sure that the DC-power supply is according to the spec-
ifications given.
DO NOT USE ALTERNATING CURRENT OR MAINS POWER SUPPLY! !
The cable leading to the distributor (power supply) or safety barrier transports power to and output sig-
nal from the transmitter. Use a two conductor shielded cable with a size of at least 1.25 mm and an
outside diameter of 6 to 12 mm. The cable gland supplied with the instrument accepts these diameters.
The maximum length of the cable is 2000 metre, or 1500 metres when using the communications. This
ensures the minimum operating voltage for the instrument.
Grounding:
• If the transmitter is mounted on a grounded surface (e.g. a metal frame fixed in the soil) the shield of
the 2-wire cable may NOT be connected to ground at the distributor.
• If the transmitter is mounted on a non-conducting surface (e.g. a brick wall) it is recommended to
ground the shield of the 2-wire cable at the distributor end.
WARNING