General Catalogue - Frank W Murphy Ltd. - #19

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Text version of the page
ms5885
(supersedes ms5884 / M040301) revision D, 20th March 2003 catalogue section 20
3ST
Three point speed relay
• Three speed relays in one compact unit
• Wide operating frequency
• Engine RPM meter output
Description
The 3ST provides three independent speed relays in one compact unit. It is designed to work with an engine mounted speed transducer, typically a magnetic pickup. The 3ST measures the transducer signal frequency (which is proportional to engine speed) and compares this with three user-set trip levels. The three non-latching relays then activate or deactivate as appropriate.
Each relay circuit has a front facia LED that lights when the relay is energised. On standard units, the relay functions are designated S1 (crank), S2 (underspeed) and S3 (overspeed): all three relays are energised, and all LEDs lit, when the engine is running at normal speed - see diagram overleaf for relay/LED operation.
Nominal speed calibration and relay trip levels are set via four multi-turn potentiometers - see 'calibration' overleaf. The 3ST also features a 'meter' output, which may be used for calibration and/or engine speed indication.
The 3ST has a robust, polycarbonate case, designed for DIN rail or surface mounting. Electrical connection is by 12 screw terminals, suitable for stripped panel wires or narrow blade crimps.
Application
The 3ST is designed for use with engines, generators, pumps or any moving machinery where speed related control that requires accurate and repeatable.
Warranty
A two year limited warranty on materials and workmanship is given with this Murphy product. Details are available on request and at www.fwmurphy.co.uk/warranty.
Specification
Power supply:
voltage range, 12 V units
8 - 16 V DC
24 V units
16 - 32 V DC
power consumption
4 W typ.
Input:
voltage range
0.5 - 80 V AC rms
nominal frequency range (fo)
1 - 8 kHz.
Special 'L' (10 - 200 Hz) and
M (200 - 1500 Hz) variants
available for volume orders
Trip settings:
S1 (crank) range
10 - 45 % of fo
S2 (underspeed) range
50 - 95 % of fo
S3 (overspeed) range
100 -130% of fo
trip point hysteresis
2.5% of setting (typ.)
Outputs:
relays
SPNC (S1) and SPDT (S2 & S3)
volt free contacts,
5A max. @ 24V DC (resistive load),
2 x 105 operations
tacho/calibration
0 - 1 mA into a 75 Ohm moving
coil meter. Output at normal
engine speed = 0.75 mA
General:
operating temperature
-10 to +55 oC
dimensions (W x H x D)
50 x 75 x 110 mm
weight
approx. 190 g
MURPHY
13

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