Yokogawa DO402 Dissolved Oxygen Analyzer - Manual (Page 28)

IM 12J05D02-01E
3-8 Installation and wiring
3-4. Wiring the contact signals
3-4-1. General precautions
The contact output signals consist of voltage-free relay contacts for switching electrical appliances
(SPDT). They can also be used as digital outputs to signal processing equipment (such as a controller or
PLC). It is possible to use multi-core cables for the contact in and output signals and shielded multi-core
cable for the analog signals.
3-4-2. Contact outputs
The EXA unit’s four contact outputs can be wired to suit your own custom requirements (Figure 3-6).
In the Non-Alarm or Power Off states, contacts S1, S2 and S3 are OFF, Common (C) and Normally
Closed (NC) are in contact.
In the “Fail” or Power Off states, contact S4 is ON, Common (C) and Normally Closed (NC) are in con-
tact.
You can either use them to switch AC power, or switch a DC Voltage for digital interfacing.
Default settings
• The contact S1 is pre-programmed for high alarm function.
• The contact S2 is pre-programmed for a low alarm function.
• The contact S3 is pre-programmed for wash function.
• The contact S4 is pre-programmed for FAIL.
The three control contacts (S1 to S3) can be used for simple process control by programming their func-
tion (Chapter 5). The FAIL contact is programmed to signal a fault in the measuring loop. Always con-
nect the FAIL contact to an alarm device such as a warning light, sound annunciator, or alarm panel to
make full use of the fault detection possibilities (self diagnostics) of the EXA converter.
3-4-3. Contact input
It is necessary to use screening/shielding on the output signal cables. Screw (M3) 23 is used to connect
the shielding.
On resistance: 10Ω or less
Off resistance: 100kΩ or more
WARNING