The PMC Type 8502 Bi-directional rpm Indicator System is designed to measure the speed of rotating machinery and to provide a linear analog output signal for remote displays. Also, as an option, it will provide digital failure signals for remote alarms.

A complete system consists of three units, as follows:

  1. Sensor
  2. Signal conditioner
  3. Display

The sensor is generally a magnetic pickup which scans gear teeth and generates a frequency signal which is proportional to the speed of rotation of the machinery. As an alternative to gear teeth, the scanning target may be magnetic tape. For applications involving rotation in two directions, a water-proof, bi-directional, zero velocity, powered pickup is used. This pickup generates two signals which can be compared to obtain the direction of rotation.

The signal conditioning unit consists of two printed circuit boards. One is a power supply pc board which generates various required regulated voltages. The other is a bi-directional rpm PC board which takes the low level pulsating DC signals from the magnetic pickup and converts them to a high level -10 to 0 to +10 VDC linear output signal for remote displays. It includes direction sensing decoders with outputs, scaling options, selector circuits, meter drivers with zero and span adjustments (ahead and astern) and failure output options with disarm capability.

The display unit is typically an analog panel meter capable of displaying the bi-directional speed signal provided by the signal conditioner. Up to six remote panel meters may be powered simultaneously, with electrical span and mechanical zero adjustments on each meter. Internal illumination is also provided for night applications and AC or DC dimmer controls are available with 0 to 100% brilliance control. Various analog display options are available including various meter sizes, bar graphs, etc.

All components in the system are carefully selected for maximum quality and reliability. Printed circuit boards are CAD designed, carefully loaded and inspected, power tested, ultrasonically cleaned and conformal coated. All components of the system are interconnected and powered for full operational tests at PMC prior to shipment. Instruction manuals are included.


  • Easy installation to existing systems using magnetic tape
  • Wide air gap between pickup and target
  • Direction sensed from single magnetic pickup
  • Waterproof magnetic pickup, cable and connector
  • Senses wide speed range down to zero rpm
  • Independent zero and span adjustments
  • Drive capability for six panel meters in parallel
  • Illuminated, DIN style, high quality panel meters, scaled to suit
  • Ultrasonically cleaned and conformal coated printed circuit boards
  • Optional alarm output for input signal failure, with remote arming capability
  • Optional display of full astern on panel meters when input signal fails


Monitoring the speed and direction of rotation of:

  • Diesel Engines
  • Propeller Shafts
  • Electric Motors
  • Speed Drives
  • Pumps
  • Conveyors
  • Presses


Analog Display

  • Scales: Standard or custom scales are included
  • Movement: Pivot and spring jewels, vibration damped for sever applications
  • Travel: 240° pointer travel
  • Accuracy: 1% of full scale
  • Relative Humidity: 75% RH average for one year
  • Temperature: -20 to 60 °C
  • Housing: Dust protected with glass front
  • Mounting: Two mounting clamps are included
  • Adjustments: Zero (mechanical) and span (electrical)
  • Illumination: Standard, with single rear mounted bulb, easily replaced
  • Weight: 0.275 kg (9.7 oz)

Signal Conditioner

The signal conditioner unit consists of a power supply pc board and a bi-directional rpm PC board. Both are joined together by a small plug-in connector PC board. The complete unit is snapped into a track mounting channel which is a non-conductive, rigid, extruded PVC chassis with dual mounting slots on 2" (51 mm) centers. The mounting channel is provided long enough for both pc boards plus an additional 1/2" (13 mm) minimum on each end so that the PC boards need not be removed for mounting.

The power supply PC board may be supplied with either a 120/240 VAC input or a 21-36 VDC input. Normal power requirement is 5.7 W. AC units provide isolation between inputs and outputs. DC units are provided with input circuit reverse polarity protection. Regulated outputs are provided to terminals and connector pins, as follows:

+24 VDC 150 mA

+15 VDC 150 mA

-15 VDC 150 mA

+5 VDC 150 mA

The bi-directional rpm PC board accepts two input signals, with a range of 0 to 100,000 Hz, and generates an output signal of -10 to 0 to +10 VDC at 6 mA maximum for driving analog panel meters. Inputs may be any AC or pulsed DC signal sources generated by active or passive magnetic pickups, open collectors, frequency sources, magnetos, etc. Both input signals are compared and the larger of the two is used. The resultant signal is provided with a zero adjustment pot and separate ahead and astern span adjustment pots. The output is positive when ahead and negative when astern. An open collector output is provided and pulled low when the output signal is positive. Various ranges of input pulses for each revolution are jumper selectable on the pc board. If either input signal fails, the output reads in the ahead direction only. If both inputs fail, the output is zero.

An optional failure detection alarm is offered and becomes armed when terminal 5 is pulled low. If either input circuit fails to receive incoming pulses, an open collector is pulled low (or optional relay contact 1 form C is actuated) for each. If both inputs circuits fail to receive incoming pulses, another open collector is pulled low.


Magnetic Tape

PMC Type MRT magnetic tape provides a convenient, simple and low cost target for PMC magnetic pickups. It is offered as an alternative to split gears, shaft slots, drilled holes, individually installed magnets, etc.

The magnetic tape is a flexible permanent magnet consisting of alternating north and south poles arranged along the tape. The tape can be bonded to a rotating shaft and a magnetic pickup placed perpendicular to the tape surface. As the tape rotates, the magnets interact with the magnetic field of the pickup that then generates the pulsating DC output signals whose frequency is proportional to the shaft speed.

  • Temperature: -30 to 70°C
  • Rotational Speed: 3000 rpm maximum
  • Dimensions: 20 x 1.5 mm (0.750 x 0.059")
  • Pulse Spacing: one pulse each 9.5 mm (0.375")
  • Weight:  0.118 grams/mm (0.007 lbs/inch)
  • Installation: adhesive mounting kit provided
  • Material: chemically resistant to oils and seawater

Magnetic Pickup

The PMC Type 8540-1520 Magnetic Pickup is a zero velocity, bi-directional sensor which, when powered, generates a magnetic field. When this magnetic field is altered by a moving ferrous object (the sensor target), the sensor generates two, out of phase, pulsating DC output signals. The relation of the phase of the two signals provides the direction of rotation. When the pickup is positioned close to a target mounted on a rotating shaft, the output signals have a frequency that is proportional to rpm. The target may be gear teeth, bolts, magnets, holes or PMC magnetic tape.

  • Sensing Frequency: 0 to 20 kHz
  • Input Power: 25 mA at +5 VDC
  • Operating Temperature: -35 to 70°C
  • Recommended Air Gap: 0.035" (0.9 mm)
  • Housing Material: stainless steel
  • Housing: watertight
  • Connector: watertight, provided
  • Weight with connector: 0.155 g (5.5 oz)
  • Cable: 3 pair shielded
  • Insulation Resistance: 100 MΩ 50 VDC pin F to housing

Pickup Mounting Bracket - Adjustable

  • Material: aluminum
  • Finish: black anodized
  • MPU Mounting Hole: sized to fit MPU diameter
  • Weight Total: 0.240 g (8.5 oz)


Type 8502-9004 Bi-Directional Tachometer System Product Bulletin SB-8502-9004



TEL (604) 433-4644    FAX (604) 433-5570    email:info@pmc-controls.com