22 Discrete I/O Modules
Publication 1746-IN005A-US-P
(6)Fast turn-off modules (1746-OB6EI, -OBP8 Series B and later, -OB16E Series B and
later, -OBP16, and
-OVP16) provide fast OFF delay for inductive loads. Comparative OFF delay times for
1746-OB8/-OV8 and fast turn-off modules; when switching Bulletin 100-B110 (24W
sealed) contactor, are: 1746-OB8/-OV8 OFF delay = 152 ms; fast turn-off modules OFF
delay = 47 ms.
(7)To limit the effects of leakage current through solid state outputs, a loading resistor can
be connected in parallel with your load. For transistor outputs, 24V dc operation, use a
5.6K
Ω
, 1/2W resistor.
(8)Recommended surge suppression: For transistor outputs when switching 24V dc
inductive loads, use a 1N4004 diode reverse-wired across the load (also see footnote 9).
Refer to the
SLC 500 Modular Hardware Style Installation and Operation Manual
,
publication 1747-6.2, for more information on surge suppression.
(9)Fast off delay for inductive loads is accomplished with surge suppressors on the 1746-
OB6EI, -OBP8 Series B and later, -OB16E Series B and later, -OBP16, and -OVP16
modules. A suppressor at the load is not needed unless another contact is connected in
series. If this is the case, a 1N4004 diode should be reverse wired across the load. This
defeats the fast turn-off feature.
(10)Repeatability is once every 1s at 30°C. Repeatability is once every 2s at 60°C.
!
ATTENTION: A transient pulse occurs in transistor outputs
when the external dc supply voltage is applied to the output
common terminals (e.g., via the master control relay). This can
occur regardless of the processor having power or not. For most
applications, the energy of this pulse is not sufficient to energize
the load. Refer to the SLC 500 Modular Hardware Style
Installation and Operation Manual, publication 1747-6.2, for
more information on transient pulses and guidelines to reduce
inadvertent processor operation.
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