As-found / as-left calibration worksheet

Download the free 5-point worksheet

How do you run an as-found / as-left check?

1. Get permission and isolate. Follow lockout/tagout and operations authorization; put the loop in manual or bypass so the control system is not affected.
2. Record the setup. Tag, configured range (LRV and URV), output range, action, transfer function, tolerance and its basis, and the reference standard with its calibration due date.
3. Work out expected values. For each test point the expected input is LRV + point% × span, and the expected output is the signal for that input — 4, 8, 12, 16 and 20 mA on a linear 4–20 mA output. The scaling calculator gives them for any range, including square root.
4. Run as found, before any adjustment. Apply each input, let it settle and write down the observed output. Going up to 100% and back down to 0% captures hysteresis.
5. Calculate each point. Error = observed − expected; percent-of-span error = error ÷ output span × 100; pass if its absolute value is within tolerance.
6. Adjust only if allowed and needed, following the manufacturer’s procedure, and note exactly what you changed.
7. Run as left with the same points, then return the loop to service and sign the record.

Worked example: a 0–200 psi transmitter with a ±0.5% of span tolerance

The output is 4–20 mA (span 16 mA). You source pressure with a calibrated hand pump and gauge and read the loop current with a meter.

As found

Worst point: 75% at 0.812% of span. Four of five points exceed 0.5%, and every reading is high by a similar amount, with the error growing a little toward the top — a zero shift plus a small span error. The instrument was out of tolerance as found, which matters for the product made since the last check.

As left, after a zero and span trim

Worst point after adjustment: 25% at 0.125% of span, well inside the tolerance. The record now shows both the condition you found and the condition you left, which is what an auditor or the next technician needs.

What does a 5-point check record, and why each field matters

• Expected and observed output at each point — the raw evidence; keep at least two decimals on mA readings.
• Error in signal units and in percent of span — percent of span lets you compare instruments with different ranges against one tolerance.
• Direction (up or down scale) — the difference between the up and down reading at the same point is the hysteresis.
• Tolerance and its basis — ±0.5% of span and ±0.08 mA are the same limit on a 16 mA span, but the record must say which one you applied.
• Reference standard and due date — a check is only as good as the instrument you checked it against; Fluke’s pressure-calibration note cites a common 4:1 ratio between the tolerance and the standard’s uncertainty.
• Adjustment notes — zero or span trim, sensor trim, parts replaced; without them, as-found and as-left numbers cannot be explained later.

How does My LoopCal produce the worksheet?

Enter or pick the instrument’s range, choose three-point, five-point or a custom set of 2–21 points, and set the tolerance as percent of span, signal units or engineering units. The app lists each expected input and output; you type the observed reading and it computes the error, percent-of-span error and pass/fail at once, then summarizes the worst point and maximum error. Run as found, record your adjustment notes, run as left, and export the PDF worksheet with your company name and logo in US Letter or A4, plus CSV.

A new install includes one guided three-point as-found check with its full worksheet on screen. Five-point and custom procedures, hysteresis, as-left runs, saved instruments with due-date reminders, and PDF or CSV export need an in-app purchase. The signal converter and loop power utilities stay free. The app runs offline with no account.

My LoopCal is a calculation aid and field worksheet — not a calibrator, an accredited calibration service, or a replacement for manufacturer procedures. Always follow site lockout/tagout, operations authorization, device manuals and approved procedures.