OPTO 22 SNAP PAC R SERIES, Руководство пользователя

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TROUBLESHOOTING I/O MODULES: FREQUENTLY ASKED QUESTIONS
SNAP PAC R-Series Controller User’s Guide 62
The solution to this issue is to place a power resistor, sized for 8–10 times the rated maximum leakage current
for the module, in parallel with the load. Make sure that this resistor has a high enough power rating for the
application.
Q: I have a new AC output driving a solenoid. It turns on once, but will not turn on again. What is
going on?
A: Some loads, like certain solenoids, some types of halogen lights, and some types of strobe lights
incorporate a diode in series with the coil or filament. This causes the load to behave as a half-wave rectifier.
Opto 22 output modules have a built-in R-C snubber circuit in parallel with the output. The capacitor in this
circuit charges up but cannot discharge through the series diode, causing a voltage to appear across the
output terminals. Because the module must see a zero voltage across the terminals to come on, it can’t turn
on again in this situation.
The solution is to find a lamp or solenoid that does not have an internal diode; a potential work-around would
be to put a high-value resistor (several tens of kilohms) across the output terminals of the module, to allow the
capacitor to drain.
Q: I have an AC output module in a circuit, wired in series (ANDed) with another contact. When that
other contact closes, my load turns on momentarily, even though my output module is off. Is my
module broken?
A: This situation arises when the output module does not see a voltage across its terminals. This occurs when
another contact is wired in series with the module, between the module and the “hot” side of the supply.
Because the module is totally isolated from field to logic, the field (or contact) side of the module must power
itself from the attached line. Because of the pilot circuit in the module, the switching semiconductor is in an
indeterminate state when there is no voltage across the module. It may turn on for up to a half cycle if it
suddenly receives power. The pilot circuit realizes that the module is on but cannot turn it off until the voltage
crosses zero again.
There is no easy solution to this issue. Typically a solution involves either maintaining a minimal voltage across
the module, pre-wetting it with a low voltage, or absorbing the energy from the half-cycle turn-on with an
R-C network in parallel with the load.
Q: Why are all four loads connected to my SNAP output module coming on when I’m activating only
one of the channels?
A: The SNAP digital output is likely connected on the wrong side of the loads. Remember that all four channels
share one fuse; thus one side of each output is common with one side of all the others. If the module is on the
wrong side of the load, any one channel is effectively connected to all four. If the output is a SNK type, try
switching to a SRC type, or vice versa. In AC applications, reverse the module wiring.
Q: I keep having failures on one channel of my SNAP output module. Why might this be happening?
A: Failures of only one of the four output channels would indicate an issue with the load being driven by that
channel. Make sure that the load characteristics, including transients, do not exceed the specifications of the
module. Also be sure that the module is properly transient protected, using either an R-C snubber (AC) or a
commutating diode (DC) across the load. Modules may also be protected through the use of transient voltage
suppressors across the module itself.
SNAP Analog Troubleshooting
SNAP analog modules require a fairly substantial amount of current due to their onboard isolation power
inverters. Because of this, it is important to make certain that the entire SNAP installation is supplied with 5.0
to 5.2 V, even while under full load.
An insufficient power supply really means a power supply that cannot provide the full load current required by
the brain and modules, or a power supply that is not adjusted to provide 5.00 to 5.20 VDC as measured at the