Dwyer application note: Dwyer Instruments FAQ: Differential Pressure Gauges, Multimeter Pricing & Calibration

I've been selecting, installing, and troubleshooting Dwyer instruments for about eight years. In that time, I've ordered the wrong pressure range on 10 transmitters, cracked a differential pressure gauge on startup by ignoring static pressure limits, and spent three hours chasing a 4-20 mA "fault" that was actually a $10 multimeter lying to me. So these are the questions I wish someone had answered for me before I made those mistakes.

What does Dwyer manufacture, and how should I use the Dwyer website?

Dwyer is one of the most recognized names in industrial measurement. They make pressure transmitters, flow meters, differential pressure gauges, humidity sensors, level transmitters, air velocity sensors, and temperature sensors. If it's a process variable you need to monitor, chances are Dwyer has a product for it.

The Dwyer website (dwyer-inst.com) is a solid place to start. You can download datasheets, check cross-references, and browse technical manuals. What I'll say honestly: it's a research tool, not a simple storefront. You'll probably order through a distributor, and that's fine. What matters is nailing down the exact model and options before you spend money.

I learned that the hard way in 2022. I skimmed a spec table on the Dwyer website, saw a "range" dropdown, figured the default was probably fine, and submitted the order. It wasn't fine. We ended up with 10 transmitters that couldn't do the job. Rework cost about $1,400 and a two-week delay. Now I open the full datasheet and check every single line. If anything feels off, I call someone.

How do I choose the right Dwyer differential pressure gauge?

This is the question I get more than any other. The Dwyer Magnehelic differential pressure gauge has been the industry standard in HVAC and filter monitoring for decades, but it's not a one-size-fits-all purchase. Check four things:

• Range. Dwyer offers everything from 0-0.5" WC up to 0-100" WC. Pick a range where your normal operating point sits in the middle third of the scale. If your reading sits in the bottom 10%, you're throwing away accuracy.
• Media compatibility. The standard Magnehelic is meant for air and compatible gases. If you're working with corrosive vapor, moisture, or liquids, you need a different setup.
• Maximum static pressure. I missed this one in my first year. A differential pressure gauge has two pressure inputs, but each side also has a static pressure limit. On a baghouse application, I mounted a Magnehelic without checking that rating. The window cracked on startup. $150 gone, and a lesson I won't forget.
• Accuracy. Standard Magnehelics run about ±2% of full scale. For critical cleanroom or filter monitoring, the Mark II series gets you to 0.5%.

And here's my rule when a deadline is breathing down my neck: don't grab whatever is in stock just to keep things moving. The wrong gauge means a reorder, a delay, and a process running unmonitored in the meantime. The right gauge, ordered once, is always cheaper.

Is a $10 multimeter good enough for instrument work?

When I first started in this field, I assumed a $10 multimeter was basically the same as any other meter. Volts, amps, ohms—what's the difference, right? A few false diagnoses later, I learned the difference is huge.

A basic $10-15 multimeter is fine for batteries, continuity checks, and seeing if a wall outlet is live. I own one. It sits in my garage drawer and does that job well.

But for troubleshooting 4-20 mA loops and transmitter signals, a budget meter can be an active liability:

• Resolution. A loop signal only spans 16 mA (4 to 20). You need to see changes of 0.01 mA to diagnose drift or wiring issues. Many cheap meters only show 0.1 mA, which is a 6% error on a 16 mA span.
• Burden voltage. Inexpensive meters can drop voltage across their own current shunt, loading the loop and skewing the reading even further.

In 2021, a colleague spent most of a shift convinced a pressure transmitter was faulty because his budget meter read 10.8 mA when the process should have been around 12 mA. We bench-tested the transmitter—it was fine. The meter was the problem. That goose chase cost more in labor than a decent multimeter costs in dollars.

Bottom line: keep the $10 meter in the garage. Don't trust it with live process signals.

Is the Fluke 175 True RMS multimeter worth the price?

The Fluke 175 True RMS multimeter is one of those tools that looks expensive until you've seen what a bad measurement costs. Then it looks like a bargain.

True RMS matters because industrial electrical signals aren't clean sine waves anymore. VFDs, motor drives, and switching power supplies all distort waveforms. A regular average-responding meter can read 10-20% low on those. The 175 reads the actual value, no guesswork.

Do you need true RMS? If you only check standard utility power, no—save your money. If you work anywhere near VFDs or modern electronic loads, yes. It's worth it.

I have mixed feelings about premium tool pricing. Part of me still flinches at spending around $400 on a multimeter when a $40 one handles household wiring just fine. But after 2021, my math changed. When a line is down and a client is waiting, the certainty of a correct reading is worth the premium. (Prices as of early 2025; verify current rates.)

I bought a Fluke 175 in early 2024. It's the first multimeter I've owned that I don't second-guess.

How do you calibrate an Eppendorf pipette?

This question shows up in every calibration training I've ever run, because someone always has a lab nearby that uses pipettes. The standard method for an Eppendorf pipette—or any micropipette—is gravimetric:

1. Set the pipette to the target volume (say, 100 µL) and make sure the tip is clean and properly seated.
2. Use distilled or deionized water at 20-25°C. Water's density at that temperature is a known, traceable reference.
3. Dispense into a weighing boat on an analytical balance with 0.01 mg resolution.
4. Record each weight, then repeat at least 10 times. Not five. Not "until it looks consistent." Ten.
5. Calculate the mean and standard deviation.
6. Compare against the accuracy and precision limits in ISO 8655.
7. If it's out of tolerance, clean or replace the seals, or send it back for service. After any adjustment, repeat the full 10-dispense verification.

I watched someone skip the repetition step in 2023 because they were short on time. They adjusted a pipette based on one single weighing. The pipette over-dispensed for weeks before anyone caught it, ruining a whole set of samples. That was about $600 in wasted materials plus a very awkward conversation with the lab supervisor.

Calibration isn't about getting one good reading. It's about proving the instrument will keep producing good readings, consistently, when it actually matters.

How often should I recalibrate Dwyer pressure instruments?

There's no universal answer, but here's a sane starting point: every 6-12 months for process-critical transmitters, yearly for HVAC sensors and panel gauges, and before any job where you can't afford surprises.

More important than the interval is the log. In October 2022, our calibration records caught a Dwyer pressure transmitter that had drifted about 3% over six months. Nothing on the panel looked wrong—just slightly off. But 3% was the line between acceptable and reject in our process. If we'd deferred calibration, we'd have shipped a bad batch and found out about it in an audit, not on the bench.

So honestly, calibration feels like a pain. It costs money, it takes time, and it's easy to put off. But the cost of discovering a sensor problem during a quality audit is ten times the cost of finding it during routine calibration. I've made that mistake once, and I don't plan on repeating it. Pay for the certainty.