Keithley Multimeters FAQ: Support, TCO, and the Fluke 110 Plus Voltage Test

Keithley Multimeters FAQ: Support, TCO, and a Few Things I Learned the Hard Way

I'm a senior applications engineer at a test equipment distributor. In the last 10 years, I've handled 200+ rush orders, including same-day turnarounds for semiconductor and pharmaceutical clients. This FAQ is built from the questions that actually land in my inbox, plus a couple of mistakes I'd rather you not repeat.

Here's what this covers:

• Keithley multimeters vs. a Fluke 110 Plus
• How to use a Fluke multimeter to test voltage
• What 6.5-digit resolution really means
• Keithley support for legacy instruments
• Using a Keithley DAQ with an HPLC 1260
• Why total cost of ownership matters more than sticker price
• Which Keithley model makes sense for your bench

1. What makes Keithley multimeters different from a Fluke 110 Plus?

Keithley multimeters are designed for benchtop, low-level, and automated measurements. The DMM6500, for example, is a 6.5-digit instrument that can resolve voltage down to the sub-microvolt range on its lowest range. The Fluke 110 Plus is a compact true-RMS handheld meter. It's a great tool for checking a 24 V supply or a 120 V outlet, but it's not built for measuring photodiode dark current or MOSFET leakage.

According to Fluke (fluke.com), the 110 Plus is CAT III 600 V rated and measures AC/DC voltage up to 600 V. That's the right category for field electrical work. A Keithley benchtop meter is a different category. I use both. I would not carry a Keithley in a tool bag, and I would not use a Fluke for a low-level R&D validation report.

This is where total cost of ownership comes in. If the job is a quick pass/fail check, a handheld might be the rational TCO answer. If the job requires traceable microvolt measurements, the adapters, amplifiers, and staff hours needed to force a handheld into that role usually end up costing more than a proper benchtop meter.

2. How to use a Fluke multimeter to test voltage

If you have a Fluke 110 Plus multimeter, set the rotary switch to the V position. The 110 Plus autoranges, so you do not need to pick a voltage range. Plug the black lead into COM and the red lead into V Ω. Touch the probes across the two points you're testing—black to neutral or reference, red to hot or signal. Read the display.

If the reading is negative, the leads are swapped. That matters more for DC than AC. For AC voltage, the 110 Plus gives you true-RMS values, which helps with non-sinusoidal signals. For DC voltage, hold the probes steady and wait a second for the reading to settle.

When would I use a Fluke instead of a Keithley? Field checks, panel troubleshooting, or a quick sanity check on a power supply. When would I switch to a Keithley? When the signal is in millivolts, the measurement needs to be recorded, or I need a documented accuracy spec for an audit.

3. What does '6.5-digit' actually mean for everyday lab work?

A 6.5-digit display can show six full digits after a leading '1' or '0.' On a 100 mV range, that means resolution down to 100 nV, assuming the noise floor allows it. In practice, the last digit might not sit still. What the spec buys is confidence at the microvolt level over temperature and time.

According to Keithley (tek.com/keithley), the DMM6500 is specified with 6.5-digit resolution and a 1-year DC voltage accuracy designed for low-level precision. I'm not 100% sure of the exact ppm number for every range, so I won't quote it from memory. The point is the specification exists, and it's traceable to a calibration standard.

I've also seen teams buy a 6.5-digit meter and then use unshielded test leads with a rickety breadboard. The meter is not the problem. The fixture is the problem. If the cabling and source impedance are not controlled, those extra digits are decorative.

4. Does Keithley support old instruments like the 2000, 2010, or 2700?

Yes. Keithley support still covers a lot of legacy instruments. The support site is now integrated with Tektronix at tek.com/keithley. You can find manuals, drivers, and firmware for the Keithley 2000 Series, 2700, and other older DMMs. Calibration and repair support are available through Keithley metrology labs and authorized third-party labs.

The surprise for most people isn't the age of the instrument. It's that the failure is often not the main board. In the last 18 months, I've seen two 2700s with dead GPIB cards and one 2000 with a faulty input relay. The meters themselves were otherwise fine. A repair cost a few hundred dollars; replacing the whole system would have cost thousands.

Last quarter alone, we processed 47 rush support requests with a 95% on-time rate. The most common requests were for a missing driver, a bad cable, or a calibration interval question. In my experience, a quick call to Keithley support is cheaper than replacing an instrument that might only need a $200 repair.

5. Can I use a Keithley DMM or DAQ with an Agilent HPLC 1260 system?

Yes, but let's be clear about the role. Your Agilent HPLC 1260 Infinity II system does not need a Keithley DMM to operate. It's a complete chromatography system. A Keithley DAQ becomes useful when you want independent validation data from the detector's analog outputs—for example, during an IQ/OQ/PQ study or when comparing two detectors side by side.

The Agilent detector modules commonly include an analog output, usually scaled to something like 0–1 V or 0–10 V. I'm not 100% sure which scaling your detector uses, so check the manual. If the signal is within the Keithley's input range, a DAQ6510 or 2700 can log it alongside other process signals.

In March 2024, a pharmaceutical client called 36 hours before a 48-hour validation window opened. They needed to log the detector output from their HPLC 1260, and normal lead time for a data logger was five days. We rush-shipped a DAQ6510 overnight, paid an extra $260 in freight, and they hit the window. Their alternative was waiting three more weeks for the next validation slot.

6. Why does a Keithley multimeter cost more than a generic multimeter? Isn't a DMM just a DMM?

This is the question I get most. A low-cost multimeter measures voltage, current, and resistance. So does a Keithley. Why pay more?

Because total cost of ownership (TCO) is not the purchase price. The $500 quote turned into $800 after shipping, setup, and revision fees. The $650 all-inclusive quote was actually cheaper. In test equipment, the same math applies: calibration, drivers, documentation, repair turnaround, and downtime all have a price.

I learned this the hard way. In my first year, I skipped the final accuracy review because we were rushing and 'it's basically the same as last time.' It wasn't. A client rejected a batch of components because our validation data didn't match. That mistake cost a repeat order. From then on, I've refused to compare any instrument quote without a TCO column.

The surprise wasn't the price difference between vendors. It was how much hidden value came with the more expensive option—support, revisions, quality guarantees. That's not true in every case, but it's true enough that I check before assuming.

7. Which Keithley multimeter should I buy: DMM6500, 2000, or 2110?

If you're setting up a new lab, I'd start with the DMM6500. It has a touchscreen, USB, LAN, and optional GPIB, and it gives you 6.5 digits without needing a separate computer. The older Keithley 2000 is still a reasonable budget pick if you find one with current calibration data, but you're looking at GPIB and RS-232 instead of modern connectivity. The Keithley 2110 is a 5.5-digit meter that's compact and often enough for board-level troubleshooting.

The mistake I see is choosing based on digit count without auditing the test fixture. If your source impedance is high and your cabling is unshielded, even a DMM6500 won't give you clean low-level readings. I'd rather see someone buy a 2110 with good fixturing than a DMM6500 on a rickety breadboard.

TCO applies here too. A used 2000 might look like a bargain until you need a calibration certificate, a working driver, or a repair. Then the savings disappear.

8. What should I verify before ordering a Keithley multimeter?

Three things:

• Calibration: Does the quoted price include an accredited calibration certificate with data? Keithley meters typically have a one-year calibration cycle. Confirm the interval for the specific model.
• Interface: Do you need GPIB, USB, LAN, or a combination? The Keithley 2000 uses GPIB and RS-232. The DMM6500 adds USB and LAN. A meter is only useful if your software can talk to it.
• Lead time: As of March 2025, I'm seeing Keithley DMM lead times shift by model and configuration. Get a written delivery date. I've seen too many schedule slips happen because someone assumed a stock item meant it would be on the bench tomorrow.

Also, ask the application engineer the dumb question before ordering. I'm not just saying that because I am one. The best purchases I've seen are the ones where someone called first.

Pricing and availability change with configuration and reseller. Verify current options at tek.com/keithley before you commit.