A Practical 5-Step Guide to Verifying WIKA A-10 Pressure Transmitter Accuracy Before Installation

Who Should Use This Checklist (And When)

This is for engineers and technicians staring at a WIKA A-10 pressure transmitter, wondering if the stated accuracy on the box will hold up in their actual process. It's for the moment right before you install—when a five-minute check can save a five-hour problem.

I've been handling instrumentation orders for 6 years now. In my first year (2017), I made the classic mistake of trusting the datasheet headline number without reading the fine print. The result? A $3,200 order had to be re-spec'd because the transmitter's accuracy at the extreme of its range didn't meet our process requirements. This checklist is what I wish I'd had that day.

Three things you'll get from this:

• A step-by-step process to cross-reference published specs with your actual conditions.
• The one parameter most people skip—and why it costs you.
• How to use WIKA's technical documentation to avoid a costly mismatch.

Step 1: Deconstruct the Datasheet Accuracy Statement

Every WIKA A-10 datasheet has an accuracy spec. It looks simple. It's not.

Let's take a typical line: "Accuracy: ≤ 0.5 % of span." Sounds straightforward, right? But there are two traps you need to check.

Trap 1: Is it % of span or % of reading? The A-10 usually specifies % of span. That means the error is a fixed percentage of the transmitter's full range, not the measured value. If you're measuring at the low end of the range, the error is larger relative to your reading. I once saw a spec claim "0.5% accuracy"—but it was 0.5% of span, and our process operated at 10% of span. The effective accuracy was 5% of reading. Acceptable? Not for our control loop.

Trap 2: What conditions are assumed? The headline number is valid only under reference conditions (usually 23°C ±2°C, no vibration, specific supply voltage). Your installation will not be those conditions.

Your task here:

• Find the accuracy statement on the datasheet.
• Note whether it's % of span, % of reading, or % of URL (upper range limit).
• Look for the reference conditions footnote. Write them down.

This took me about 45 seconds once I learned where to look. The datasheet for the A-10 has a clear table on the second page.

Step 2: Calculate Your Worst-Case Error (At Your Operating Point)

This is where the math happens. Don't skip it.

Formula:

Worst-case error = (Accuracy % / 100) × (Full range)

Example:

• Transmitter range: 0-100 psi
• Accuracy: 0.5% of span
• Your operating point: 20 psi
• Worst-case error = (0.5 / 100) × 100 psi = 0.5 psi
• That 0.5 psi is 2.5% of your actual reading at 20 psi.

Does that matter for your process? Maybe. For a tank level application, 2.5% might be fine. For a critical pressure safety interlock? Probably not.

Pro tip: I keep a quick calculation in my notebook. It's faster than pulling up Excel every time. Just a simple table with common operating points and their effective error.

Step 3: Apply Temperature Effects (The One Most People Skip)

Here's the step I ignored in 2017. The A-10 datasheet will have a temperature coefficient—usually something like "≤ ±0.2% of span per 10K change in ambient temperature."

This is where your installation environment matters. If your process is in a conditioned control room, fine. If it's on a sunny pipeline in Houston in August, you have a problem.

How to calculate temperature error:

1. Find your expected temperature variation from reference conditions. Reference is usually 23°C. If your process area hits 40°C, that's +17K.
2. Divide by the spec interval (10K). That gives you ~1.7 intervals.
3. Multiply by the temperature coefficient. 1.7 × 0.2% = 0.34% additional error.
4. Add that to your basic accuracy. 0.5% + 0.34% = 0.84% total potential error.

Suddenly, your "0.5%" transmitter is effectively 0.84% in your installation. And that's before we talk about vibration or supply voltage.

I still kick myself for not doing this on that $3,200 order. If I'd applied temperature effects first, I'd have ordered the A-10 with the extended temperature compensation option. $45 more on the PO. Worth every penny.

Step 4: Check the Calibration Certificate Against Your Application

Every WIKA A-10 comes with either a standard factory calibration or, if you paid for it, a traceable certificate. Most people just file it. Don't.

Here's what to verify:

• Is the calibration performed at the range you ordered? A 0-100 psi transmitter calibrated at 0-100 psi is fine. One that was calibrated as a standard 0-100 psi but your application requires a 0-50 psi turndown? The accuracy spec changes. Check the datasheet for turndown effects.
• Are the test points relevant? The standard certificate usually does 5 points (0%, 25%, 50%, 75%, 100%). If your operating point is at 10% of range, you're outside the verified range. Not ideal. Consider requesting additional points.
• Is the as-found data acceptable? Compare the as-found calibration results against the claimed accuracy. If the transmitter passed but barely, and your process is tight, maybe this unit isn't the best one.

I have mixed feelings about this step. On one hand, it's a 5-minute check. On the other, if you don't have the certificate handy (it's often emailed separately from the physical shipment), it's easy to skip. I make it a rule now: the transmitter doesn't leave the receiving dock until I've seen the cert.

Step 5: Perform a Quick Incoming Inspection (The Confidence Check)

This is your last line of defense. You don't need a full re-calibration—just a functional check to catch gross errors.

What you'll need:

• A stable pressure source (a hand pump or deadweight tester).
• A reference standard (at least 4x more accurate than the transmitter).
• 24V DC power supply (or whatever the A-10's loop-powered voltage requires).

The 3-point check:

1. Apply 0% pressure. Read the output. Should be 4 mA (or 0 VDC). Note the deviation.
2. Apply 50% pressure. Read the output. Should be 12 mA (or 50% of voltage span).
3. Apply 100% pressure. Read the output. Should be 20 mA (or full voltage span).

Each point should be within the accuracy spec we calculated back in Step 1 and Step 3 combined. If it's not? That's your flag. Don't install it—return it.

One more thing: Check the physical condition. Bent process connection? Scratched diaphragm? It might have been damaged in shipping. I caught one once where the pressure port was dented. The inside looked fine, but I sent it back anyway. Not worth the risk.

Common Mistakes to Watch For

I've made most of these. You don't have to.

• Trusting the headline number. Accuracy is never just one number. You need the full context.
• Skipping the temperature calculation. This is the one I see most engineers miss. Your installation temperature matters.
• Ignoring the calibration certificate. It's not just paperwork. It's your first piece of evidence that the transmitter will do what it says.
• Not documenting your checks. I use a simple form now. Date, transmitter serial number, three test points, pass/fail. It's saved us in audits more than once.

Quick final thought: The WIKA A-10 is a solid transmitter. I've installed dozens. But solid doesn't mean bulletproof. A five-minute check—using this list—can prevent a day of troubleshooting and a potential process upset. That's worth the time.