YWRVL4 (spco)


  • Din rail mounted
  • SPCO output
  • Detection of machine underspeed, stopping, jamming
  • Suitable as a watchdog relay with PLC’s
  • Choice of NAMUR, PNP or clean contact inputs
  • Transformer isolation from sensor input circuit
  • Auto reset
  • Without start up time delay
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Din rail mounted underspeed relays suitable for all kinds of machinery to detect loss of speed and pulse continuity. These units are useful when an output contact is required to alarm on jamming, loss of speed due to blunt cutting tools or as a “stationary” contact to allow the release of machine guards. Applications also include being used as “watchdog” relays.

The input is achieved from either a NAMUR proximity switch, PNP sensor or from a clean contact. Unlike the unit type YWRVL the YWRVL4 does not energise for approximately 8 seconds on the initial connection of the coil voltage, but will energise when the first leading edge of an input is seen. Thereon the operation is “time based” an input will reset the time delay, if an input is not seen within the set time the output relay will de-energise but not latch. Therefore the unit will re-energise if a new leading edge of an input is seen. Removal of the coil voltage, failure of the sensor, or a breakage in the cable between the unit and the PLC or sensor will also cause the output relay to de-energise if in an energised state. Hence the underspeed monitor is fail safe.

The choice of sensor depends on the speed of the equipment and the time between impulses. To determine the controlling time it is necessary to calculate the time between two impulses at normal speed. This time will be:-

T = 60 / n.V

V = Speed in RPM

n = Number of teeth

For higher speeds one impulse per revolution would be sufficient, but for very low speeds it may be necessary to have a higher number of impulses per revolution in order to achieve a reasonable operating time. It should also be noted that at maximum speed the number of impulses received must be less than 18000 per minute (300Hz). Therefore, the maximum number of impulses per revolution is:-

n.max = 18000 / V.max

The proximity sensor (NAMUR and PNP) is isolated from the coil voltage by means of a transformer. On DC coil voltage versions there is no isolation.

Supply & Measuring

Nominal supply tolerance: ±15%

Max Power Consumption: 11VA

Repeat accuracy:
±0.5% at constant ambient
±3% across temperature range

Reset time: 100 mSec on make

Input signal:
NAMUR proximity switch
PNP sensor (max 20mA)
Normally open contact (8VDC, 8mA)

Max operating speed: 300Hz (18,000 RPM)

Min impulse: 1mSec

Min time between impulses: 1mSec

Via 4 sub time ranges, specify range S, M or L

Special 12 hour & 24 hour units also available

Relay outputs

Output contacts: SPCO units 10Amps/250V AC1

Mechanical life: 30 Million ops

Electrical life: 200K ops at max rated load


Operating temperature: -20°C to +65°C

Storage temperature: -20°C to +65°C

CE marked: Yes

In accordance with:
EN61000-6-1: 2007
EN61000-6-3: 2007
EN61010-1: 2002

Housing material: Polycarbonate, Auto extinguishable to UL 94 V-0


YWRVL4 (Din rail SPCO)

TIME RANGE (specify S, M or L)

S (0.06 to 160 secs)
0.06 to 0.6 sec
0.25 to 2.5 sec
2 to 20 sec
16 to 160 sec

M (0.5 sec to 21 mins)
0.5 to 5 sec
2 to 20 sec
16 to 160 sec
2 to 21 mins

L (15 sec to 640 mins)
15 to 150 sec
1 to 10 mins
8 to 80 mins
64 to 640 mins

Also available are dedicated 12 hour and 24 hour versions, as supplied to detect jamming and loss of flow on rotating sewage beds.




*On DC auxiliary supply versions the proximity sensor (NAMUR and PNP) is not isolated from the coil voltage.



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