SMC Networks VEX3 Series Operation Manual page 6

VEX3 Series
3 position valve with 3 ports / Precautions (2)
Be sure to read before handling.
Design/Selection
Caution
1. Leakage voltage
Take note that the leakage voltage will increase when a resistor is
used in parallel with switching element or a C-R circuit (surge
voltage suppressor) is used for protecting a switching device
because of the passing leakage voltage through the C-R circuit.
The suppressor residual leakage voltage should be as follows.
DC coil
3% or less of rated voltage
AC coil
●VEX3121, VEX3122, VEX3221, VEX3222
VEX3321, VEX3322, VEX3421, VEX3422
●VEX3501, VEX3701, VEX3901 } 15% or less of rated voltage
2. Solenoid valve drive for AC with a solid state
output (SSR, TRIAC output, etc.)
1) Current leakage
When using a snubber circuit (C-R element) for surge
protection of the output, a very small amount of electrical
current will continue to flow even during the OFF state.
This results in the valve not returning. In a situation where the
tolerance is exceeded, as in the above case, take measures to
install a bleeder resistor.
2) Minimum allowable load amount (Min. load current)
When the consumption current of a valve is less than the
output's minimum allowable load volume or the margin is small,
the output may not switch normally. Please contact SMC.
3) Solenoid valve with full wave rectifier circuit
When the solenoid valve built-in full wave rectifier circuit with
the AC specifications is used, the solenoid valve return failure
may occur depending on the kind of the triac output circuit.
Carefully check this point when selecting a SSR or sequencer.
For details, contact the SSR or sequencer manufacturer.
3. Surge voltage suppressor
1) A surge voltage suppressor built into the valve is intended to
protect the output contacts so that the surge generated inside
valve does not adversely affect the output contacts. Therefore,
if an overvoltage or overcurrent is received from an external
peripheral device, the surge voltage protection element inside
the valve is overloaded, causing the element to break. In the
worst case, the electric circuit enters the short-circuit status by
the breakage. If the energizing continues in this status, a large
current flows. This may cause secondary damage to the output
circuit, external peripheral device, or valve, and may also cause
fire accident. So, take appropriate protective measures, such
as installation of an overcurrent protection circuit in the power
supply or drive circuit to maintain the sufficient safety.
2) If a surge protection circuit contains nonstandard diodes, such
as Zener diodes or varistor, a residual voltage that is in
proportion to the protective circuit and the rated voltage will
remain. Therefore, take into consideration the surge voltage
protection of the controller.
In the case of diodes, the residual voltage is approximately 1V.
4. Surge voltage intrusion
(For VEX3121, VEX3221, VEX3321, and VEX3421)
With non-polar type solenoid valves, at times of sudden
interruption of the loading power supply, such as emergency
shutdown, surge voltage intrusion may be generated from
loading equipment with a large capacity (power consumption),
and the solenoid valve in a deenergized state may switch over
(see Figure 1).
When installing a breaker circuit for the loading power supply,
consider using a solenoid valve with polarity (with polarity
protection diode), or install a surge absorption diode between the
loading equipment COM line and the output equipment COM line
(see Figure 2).
8% or less of
rated voltage
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VEX-OMT0003