11RVL, 8RVL (spco), 11RVLMP (spco)


  • 8 & 11 pin plug in
  • SPCO output
  • Detects machine underspeed, stopping, jamming
  • Suitable as a watchdog relay with PLC’s
  • Choice of NAMUR, PNP or clean contact inputs
  • Available auto or manual reset
  • LED indication
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Simple 8 & 11 pin plug in underspeed relays suitable for all kinds of machinery to detect loss of speed and pulse continuity. These units are useful where 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 units are normally energised and are “time based” a pulse resets the time delay, if a pulse is not seen within the time range set on the front of the unit the output relay de-energises and latches out. The input circuit on the underspeed relay is looking for a change in state of input. To reset the unit the coil voltage needs to be removed for approximately 100mSec then reconnected (as an option suffix M1 can be added to the order code giving an auto reset device).

On initial connection and reconnection of the coil voltage the unit will energise for approximately 8 seconds irrespective of the rate of pulses inputting the device, this is in order to allow a stationery machine/system to run up to normal speed. Note, if M1 auto reset option is specified the 8 second run up time is not applicable, care is therefore cautioned in the choice of application that this option is specified to avoid relay chatter.

The relay will de-energise in the event of a coil supply voltage failure, failure of the sensor, breakage of the cable between sensor and the unit, hence the underspeed monitor is fail safe.

11RVL, 8RVL - The input is achieved from either a NAMUR proximity switch or from a clean contact.

11RVLMP - The input is achieved from either a NAMUR proximity switch, PNP sensor or from a clean contact. The 11RVLMP also benefits from a reset input by momentarily closing link S2 between pins 2 & 8. Note that the 8 second run up time will not be applicable and is only achieved by the connection and reconnection of the coil voltage.

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 not isolated from the coil voltage.

Supply & Measuring

Nominal supply tolerance: ±15%

Max Power Consumption: 4VA

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

Reset time: 100 mSec on make

Inhibit time on switch on: 7 to 8 seconds

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 output:

Output contact: 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


8RVL (8 pin SPCO)
11RVL (11 pin SPCO)
11RVLMP (11 pin 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, supplied to detect jamming and loss of flow on rotating arm sewage beds.





Insert M1 if auto reset is required, standard unit once switched requires the removal and reconnection of the coil voltage to achieve a reset.



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