What the Fluke 45 Dual Display Multimeter Does

ByKen

What the Fluke 45 Dual Display Multimeter Does

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The Fluke 45 is a bench multimeter with two five-digit displays. Its dual display lets one screen show a measurement in the function set on the primary display while the second screen shows another reading or a comparison result. This guide explains how the dual display works, what the two sources we opened say about its functions and accuracy, and where those sources disagree or stay silent.

Quick answer

  • The Fluke 45 has two five-digit displays. A 1990 review says the second display can show every measurement function that the primary display offers.
  • The two sources list about 16 measurement functions, true-RMS AC readings, and a 100,000-count maximum resolution at the slowest reading rate.
  • The sources do not agree in every detail about ranging on the second display, and the review is from 1990. Check the manual for the unit you own.

How we chose

The keyword names one model, so we opened two pages for it. One is a specification summary on a technical reference site. The other is a 1990 review of the meter published by a magazine. We did not use search snippets, retailer prices or star ratings. The review is much older than the summary, and its figures may describe an earlier revision of the instrument. We say where that matters.

What the dual display does

According to the 1990 review, the second display duplicates all the functions of the primary display, so the meter effectively is two 5-digit multimeters in one. The review says the primary display can be set to auto or manual ranging, while the secondary display only autoranges. That is a practical difference. If you need a fixed range on the second reading, the review’s description suggests you cannot set it on that display.

The specification summary gives less detail. It says the meter has a multifunction vacuum fluorescent dual display, and it quotes Fluke’s own line that the meter has two multifunction displays and 16 different measurement capabilities. It does not explain what each display shows by default. The two sources therefore agree that there are two displays and that both can show multiple functions, but only the review describes the ranging difference.

The review also describes a production use. Upper and lower limits can be set, and the result is shown as Hi, Lo or Pass on the second display. The specification summary lists a COMPARE mode with Hi, Lo and Pass states, along with MIN/MAX and RELATIVE modes. The two sources are consistent on the comparison function.

Functions listed

The specification summary lists 16 functions, including true-RMS voltage and current for both AC and DC, frequency, resistance and dB. The stated ranges are DC voltage from 0 to 1000 V, AC voltage from 0 to 750 V over 20 Hz to 100 kHz, DC current from 0 to 10 A, AC current from 15 µA to 10 A over 20 Hz to 20 kHz, resistance from 0 Ω to 100 MΩ, and frequency from 5 Hz to 1 MHz. The dB function is referenced to 600 Ω.

The review confirms true-RMS AC voltage and current measurement, including non-sinusoidal waveforms. It gives the sample rates as 2.5, 5 or 20 readings per second. At the slowest rate the maximum resolution is 100,000 counts. At the medium rate the review gives 30,000 counts, and at the fast rate 3,000 counts.

Interfaces also differ slightly between the two sources. The summary says RS-232 is standard, with IEEE-488.2 available as an option. The review says RS-232 is built in and that an optional IEEE-488 interface is available. Both agree on the existence of the optional bus; they do not give the same wording for the standard interface, so confirm the port list on your unit.

Accuracy as listed

The specification summary gives accuracy at the best setting and the medium reading rate. DC voltage is ±(0.025% + 2) and AC voltage is ±(0.2% + 10). DC current is ±(0.05% + 2) and AC current is ±(0.5% + 10). Resistance is ±(0.05% + 2), frequency ±(0.05% + 1), and dB ±0.08 dBm.

The review gives a different and rougher picture. It states about ±0.02% on DC voltage and about ±0.05% on DC current and resistance. For AC it says accuracy varies with frequency, and it does not give a single AC figure. The review’s DC voltage figure is tighter than the summary’s basic DC voltage figure, which may reflect a different reading rate or a different reference point. We do not choose between them. Use the accuracy table in the manual for the setting you use.

Connections and physical details

The summary gives the size as 216 × 93 × 286 mm and the net weight as 2.4 kg, or 3.2 kg with the battery. It gives a one-year warranty and a one-year calibration interval. These figures describe a bench instrument. The meter is not a pocket tool, and the sources do not describe it as portable.

The summary notes closed-case calibration and an optional rack-mount kit. Those points matter for a calibration lab or a production bench, where the unit is kept in one place and calibrated on a schedule.

What the sources do not explain

Neither source explains how to set the second display’s comparison limits step by step. The review mentions the Hi, Lo and Pass indicators, but the operating steps are in the manual, and we did not read the manual. The summary does not say which display shows the dB value, and the review does not mention dB at all.

The two displays also raise a practical question about which reading you should log. If you use both displays for two different functions, you need to know which one feeds your record. The sources do not describe a logging setup for the second display.

Step-by-step: setting up a dual-display reading

  1. Confirm the meter’s power and interface connections before you start a long reading run.
  2. Select the function on the primary display. The review says the second display duplicates the primary functions, so choose a function for each display as your task requires.
  3. Set the primary display to auto or manual ranging, depending on whether you need a fixed range.
  4. Remember that the review describes the second display as autoranging only.
  5. For a go or no-go check, set the upper and lower limits and read the Hi, Lo or Pass result on the second display.

These steps follow the behavior the review describes. The specification summary does not give a setup procedure, so treat the sequence as a starting point and confirm the menu names against the manual.

Where the sources disagree or are old

The review is from 1990. A meter with the same name may have had firmware or hardware changes since then. The summary does not give a revision date, so we cannot tell which production version it describes. That is the main reason the two sources should not be merged into one specification.

The ranging detail and the accuracy figures are the two places where the sources differ most. We report both and do not choose one silently.

What we could not verify

  • The current manual and the revision history of the Fluke 45 were not among the sources we opened.
  • The summary gives an AC voltage range to 750 V, but the review does not state the AC voltage limit.
  • We could not confirm whether the second display’s ranging limit described in the 1990 review still applies to every production unit.
  • The sources do not describe the logging or software options that go with the RS-232 or IEEE-488 interface.

FAQ

Does the second display show a different function from the first?

It can. The 1990 review says the second display duplicates all functions of the primary display, so each display can show any of the measurement functions. The two displays are set separately.

Can the second display be set to manual ranging?

According to the review, no. The second display only autoranges, while the primary display can be set to auto or manual.

Is the Fluke 45 a portable meter?

The summary gives a size of 216 × 93 × 286 mm and a net weight of 2.4 kg, which describes a bench instrument. The sources do not call it portable.

What interfaces does it have?

The sources agree that an optional IEEE-488 interface exists and that RS-232 is available on the meter. The wording of the standard interface differs between the two sources, so check the port list on your unit.

For related reading on this site, see our article on auto-ranging multimeters and our multimeter guide.

Bottom line

Read the Fluke 45 as a bench meter with two displays that can each show a measurement, with the second display limited to autoranging according to the 1990 review. Confirm the accuracy table and the interface list in the manual for your revision before you rely on either source.

Sources

  • Media College, Fluke 45 equipment page: https://mediacollege.com/equipment/fluke/45.html (opened 2026-10-30)
  • Silicon Chip, The Fluke 45 Digital Multimeter, September 1990 issue: https://siliconchip.com.au/Issue/1990/September/The+Fluke+45+Digital+Multimeter (opened 2026-10-30)

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