Digital Tachometer SELECTRONIC®

MT90 Model

• ±1 RPM Accuracy
• Easy Calibration
• Clear-Read LCD Display
• Back Light for Night Viewing (Battery Powered models)
• Input Source Can Be a Magnetic Pickup or Engine Alternator
• Power Supplied by Magnetic Pickup or 12, 24 or 32 VDC Battery System


The Murphy SELECTRONIC® MT90 is a digital tachometer. Its high accuracy and dependability result from use of a quartz crystal time based and digital, solid-state electronics.

Tachometer power is supplied by either a Murphy magnetic pickup, mounted at the flywheel ring-gear of an engine, or by a 12, 24 or 32 volt DC battery system.

RPM data is supplied by either a Murphy magnetic pickup or by the alternator in your battery charging circuit. The MT90 also has back-lighting for easy readings in low lit areas; this lighting requires a battery power source.

RPM Calibration

The MT90 is calibrated to engine RPM by setting a series of calibration rotary switches on the back of the tachometer. The proper switch sequence for the engine is determined by (1) the number of ring gear teeth for the magnetic pickup, or (2) by the ratio of alternator to engine pulley diameter, and the number of poles of the alternator.


Typical applications include: Generators, Compressors, Industrial Engines, Oil Field Equipment, Marine Vessels, Vehicles, Farm Equipment, and Construction Equipment.



Signal Input Voltage: 4 to 35 Vrms from a magnetic pickup or alternator**
Pulses per Revolution: 3 to 999
Power Requirements:
• Pickup Power: 4-35Vrms** • Battery Power: 8-40 VDC (12, 24, 32 volt)
Current: • Tach back-light Off, 4mA @ 40 VDC • Tach back-light On, 25 mA @ 40 VDC
Case: 1018 polycarbonate/polyester blend
Lens: Polycarbonate
Bezel: #430 Stainless Steel
Display: LCD, 4-digit, seven segment
Operating Temperature: -4 to 158°F (-20 to 70°C)
Storage Temperature: -13 to 185°F (-25 to 85°C)
Mounting Hole: 3-7/16 in. (87 mm.)
Shipping Weight: 14 oz. (0.4 kg)
Shipping Dimensions: 5-1/2 x 5-1/2 x 5-1/2 in. (140 x 140 x 140 mm.)

A two-year limited warranty on materials and workmanship is given with this Murphy product. Details are available on request and are packed with each unit.


* Products covered by this bulletin comply with EMC Council directive 89/336/EEC regarding electro- magnetic compatibility except as noted.

**See “Special Note” for Magnetic Pickup Powered MT90 applications (below).