Digital Tachometer and Hourmeter With Adjustable Overspeed Set Point

Model MTH6

• Tachometer and Hourmeter With Overspeed Shutdown or Alarm Switch
• Reads RPM Data from a Magnetic Pickup or Battery Charging Alternator
• Powered by 8 to 40 VDC
• Large 5-Digit LCD Display
• Maintains Hours Count When Power Is Lost
• Front Panel Programming
• Hours Can Be Reset to Zero


This microprocessor-based digital tachometer and hourmeter with a built-in overspeed switch is highly accurate and dependable. It measures speed and running hours and can give an alarm or shut down the engine on overspeed.

The MTH6 case is polycarbonate, and its dial measures 3-1/2 in. (89 mm.) in diameter.

RPM data for the tachometer and overspeed switch is supplied by a magnetic pickup or battery charging alternator. The magnetic pickup is installed into the flywheel housing of an internal combustion engine. The starter ring gear acts upon the magnetic pickup to generate a voltage pulse each time a gear tooth passes the end of the sensor.


• Industrial Engines
• Generators
• Compressors
• Oil Field Equipment
• Marine Engines
• Vehicles
• Farm Equipment
• ConstructionEquipment


Basic Operation

During normal operation, the MTH6 displays RPM. Its five-digit, liquid crystal display is updated every second. When the MTH6 is displaying hours and a speed signal is present, the far left digit and decimal point will flash indicating the hourmeter is operating.

The overspeed set point and running hours can be viewed by manipulating three membrane switches located on the MTH6 front panel.

When the overspeed set point is met an LED, also located on the front panel, lights.


The MTH6 calibration is simple. The operator enters the number of pulses per engine revolution and the overspeed set point value using the membrane-switches located on the front of the MTH6.


Power Requirements: 8-40 VDC (12, 24 or 32 VDC systems)
Maximum Current:
12 VDC: 0.011 A, backlight Off; 0.025 A, backlight On
24 VDC: 0.008 A, backlight Off; 0. 015 A, backlight On
32 VDC: 0.007 A, backlight Off; 0. 010 A, backlight On

Operating Temperature: -4° to 158°F (-20° to 70°C)
Storage Temperature: -40° to 185°F (-40° to 85°C)
Case: 1018 Polycarbonate/Polyester blend
Mounting Hole Dim.: 3-3/8 in. (86 mm.) Dia.
Speed Input: 4.5 Vrms minimum
Overspeed Switch Rating: 2 A, 50 VDC
Overspeed Range: 0 to 9000 RPM
Pulses per Revolution: 4 to 255
Tachometer Range: 0 to 65,535 RPM
Tachometer Accuracy: ±1% of the display reading or -2 RPM whichever is greater
Input Frequency Range: 25 Hz to 20 kHz
Hourmeter Range: 0 to 99999 hrs
Hourmeter Resolution: ±0.1 Hour up to 9999.9; ±1 hour 10,000 and up
Reset Hourmeter: Apply temporary ground to terminal #5 to reset hours to zero

Shipping Weight: 14 oz. (435 g)
Shipping Dimensions: 5-1/2 x 5-1/2 x 5-1/2 in. (140 x 140 x 140 mm.)

* 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).

How To Order




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.

Typical Wiring Diagram


In order to consistently bring you the highest quality, full featured products, we reserve the right to change our specifications and designs at any time.