Omron H5CX Manual page 49

Safety Precautions (H5CX-A/-L)
CAUTION
If the output relay is used beyond its life expectancy, its contacts
may occasionally become fused or there may occasionally be a risk
of fire. The life expectancy of the output relay varies considerably
according to its usage. Use the output relay within its rated load and
electrical life expectancy.
Depending on the wiring, unwanted current from the AC power
supply may occasionally burn out (damage) the internal parts.
The H5CX-A/-L (except for H5CX-A11/-A11S) do not have
transformers. Therefore, there is no insulation between the power
supply and input terminals, so make sure that wiring is correct before
use.
For the power supply of an input device of the H5CX (except for
H5CX-A11/-A11S), use an isolating transformer with the primary and
secondary windings mutually isolated and the secondary winding not
grounded.
Correct Wiring Example
H5CX
Power supply
Input
terminals
Circuit
Isolation transformer is required.
Incorrect Wiring Example 1
Do not ground the secondary winding. If the secondary wiring is
grounded, as shown in the following diagram, unwanted current may
occasionally burn out or damage the internal parts.
H5CX
Power supply
Input
terminals
Circuit
Incorrect Wiring Example 2
Do not simultaneously input signals from a single input contact or a
transistor to two or more timers that have independent power
supplies. Otherwise, the internal parts may occasionally be burnt out
or damaged by unwanted current, as shown in the following diagram.
H5CX
Power supply
Input
terminals
Input
terminals
Precautions for Safe Use
Usage Precautions
Do not touch the input terminals while power is supplied. The H5CX
(except for H5CX-A11/-A11S) has a transformerless power supply
and so touching the input terminals with power supplied may result in
electric shock.
Changing the Set Values
When changing the set value during a timing operation, the output
will turn ON if the set value is changed as follows because of the use
of a constant read-in system:
Elapsed time (UP) mode: Present value ³ set value
Remaining time (DOWN) mode: Elapsed time ³ set value
Note: When in the remaining time mode, the amount the set value is
changed is added to or subtracted from the present value.
Precautions for Correct Use
Operation with a Set Value of 0
Operation with a set value of 0 will vary with the output mode. Refer
to the Timing Charts.
Digital Timer
(The present value is set to 0.)
H5CX
49