Marmonix MMU-112 (MMU112) True RMS Digital Multimeter, 6000 Counts, 20 A

The Marmonix MMU-112 multimeter, printed as MMU112 on its front panel and also listed as MMU 112, is a 6000-count True RMS meter that measures DC voltage to 1000 V, AC voltage to 750 V, and AC or DC current from 600 µA up to 20 A. It also reads resistance to 60 MΩ, capacitance to 9.999 mF, frequency to 9.999 MHz, duty cycle, diode and continuity, plus temperature from −20 to 1000 °C with the thermocouple in the box. DC voltage accuracy is ±(0.5% + 3) and AC voltage ±(1.0% + 3). MAX/MIN, REL, HOLD, manual or auto ranging and a backlit screen sit on the front keys, and two AA cells power it. See where it fits among Marmonix digital multimeters, or work through the multimeter buyer’s guide first.

Key features

What the MMU-112 measures and records:

• 6000-count LCD with backlight
• True RMS AC measurement
• AC/DC voltage up to 1000 V DC / 750 V AC; current up to 20 A
• Resistance to 60 MΩ; capacitance to 9.999 mF; frequency to 9.999 MHz
• Temperature –20 °C to +1000 °C (with probe)
• MAX/MIN, relative, data hold, auto power-off
• Protection case and anti-broken bracket
• Safety rating CAT IV 600 V

MarMonix MMU 112 Digital Multimeter Specifications

Typical use cases

Jobs this meter is commonly bought for:

• Electrical maintenance — voltage, current, and continuity on distribution and equipment circuits
• HVAC & industrial — temperature, resistance, and frequency checks on plant systems
• Automotive diagnostics — battery, charging, and capacitance checks
• Training labs — durable demo meter with a clear display for students

What’s in the box

Supplied with the MMU-112:

• MMU-112 main unit
• Test leads
• Temperature probe
• 2 × AA batteries
• Warranty card
• Certificate of Conformity

Related reading: Multimeters · How to choose a multimeter

Buying guide: Read our digital multimeter buyer’s guide.

Case study: a pump starter that trips only some of the time

An intermittent trip on a pump or fan starter rarely shows up in a single spot reading. A 6000-count True RMS meter can stay connected and hold the extremes instead:

• Keep it awake: hold SELECT while switching on to disable the 15-minute auto power-off.
• Record the supply: on AC volts, press MAX/MIN once for the highest value and twice for the lowest, so a dip during start-up stays on screen.
• Read frequency on the same hook-up: pressing Hz % while on AC volts or AC amps shows frequency or duty cycle without moving the leads.
• Measure control current: contactor coils and sensor loops go in series on the mA/µA terminal; loads up to 20 A use the separate 20A terminal.
• Look for heat: the thermocouple input shows whether a contactor or terminal is running hot.

Before changing from volts to amps, the circuit is switched off, opened and the red lead moved to the current terminal; a current range must never be connected across a supply.

MMU-112 / MMU112: common questions

Is the MMU112 the same meter as the MMU-112?

Yes. MMU112 is the model as printed on the meter, and MMU-112 and MMU 112 refer to the same Marmonix 6000-count True RMS multimeter, part number 7603331.

Does the MMU-112 measure 20 A?

Yes, both AC and DC, through its dedicated 20A input. Smaller currents use the mA/µA input, from the 600.0 µA range up to 600.0 mA, at ±(1.2% + 3) DC and ±(1.5% + 3) AC.

Can the MMU-112 measure temperature?

Yes. With the thermocouple probe supplied it reads −20 to 1000 °C (−4 to 1832 °F) at 1 °C resolution and ±(2.5% + 5) accuracy.