Analyzer Drift – LDARtools

What This Report Does

Reports drift check results for analyzers that were drifted using the Standard drift method. A drift check is a spot reading taken during the day to verify that the analyzer is still reading accurately relative to the morning calibration. Each row shows the morning calibration reading for a cylinder, followed by the mid-day (Drift 1) and end-of-day (Drift 2) drift check readings and their percent deviation.

Use this report to verify that analyzers remained within acceptable drift limits throughout the inspection day, and to document drift results for regulatory requirements. This report is in the Calibration folder on the Reports tab.

When to use it

Reviewing morning calibration readings alongside intra-day drift results.
Confirming that drift checks were performed and that all readings passed.
Producing drift documentation for an audit or regulatory submission.
Identifying analyzers that exceeded drift limits during a period.

Parameters

Parameter	Description	Required	How it filters
Start Date	Start of the date window	Yes	Calibration dates on or after this date are included
End Date	End of the date window	Yes	Calibration dates on or before this date are included
Analyzers	One or more analyzers to include	Yes	Only records for the selected analyzers appear

Analyzer list is date-filtered. The Analyzers parameter only shows analyzers with a Standard drift record in the database for the selected date range.

Columns

Column	What it shows	Format / Notes
Analyzer	Analyzer device name	Text
Date	Date the calibration and drift checks were performed	Date; facility local time
Tech Id	Technician who performed the calibration	Text
Calibrate	Time of the morning calibration reading	Time (H:MM:SS AM/PM)
Cylinder	Cylinder label or serial number	Text
Cyl. Exp	Cylinder expiration date	Date
Conc.	Cylinder gas concentration in PPM	Integer
Reading	Morning calibration reading in PPM	Decimal
Pass	Whether the morning calibration passed	"Yes" or "No"
Drift1	Time of the mid-day drift check (Drift 1)	Time (H:MM:SS AM/PM); blank if no mid-day drift performed
Drift1 Results	Mid-day drift check reading in PPM	Decimal; blank if no mid-day drift
Pct.	Mid-day drift percent deviation	Percentage; blank if no mid-day drift
Pass	Whether the mid-day drift passed	"Yes" or "No"; blank if no mid-day drift
Drift2	Time of the end-of-day drift check (Drift 2)	Time (H:MM:SS AM/PM); blank if no end-of-day drift
Drift2 Results	End-of-day drift check reading in PPM	Decimal; blank if no end-of-day drift
Pct.	End-of-day drift percent deviation	Percentage; blank if no end-of-day drift
Pass	Whether the end-of-day drift passed	"Yes" or "No"; blank if no end-of-day drift
Ext Probe	Whether an extension probe was used	"Yes" or "No"

What's Included and Excluded

Included:

Calibration records (morning readings) for the selected analyzers within the date range.
Drift 1 (mid-day) readings matched to the morning calibration.
Drift 2 (end-of-day) readings matched to the morning calibration.

Excluded:

Analyzers not selected.
Records outside the date range.
Analyzers drifted using the VVa method — a three-reading EPA drift method (40 CFR Part 60, Appendix F, Method VVa) — those appear in the VVa Drift report.
Zero gas rows do not show drift percent values (no drift calculation for zero gas).

How Key Values are Calculated

Drift Percent

The percent deviation between the drift reading and the morning calibration is calculated according to the drift method configured in the analyzer's calibration settings:

Setting	Formula
VVa 60.485a	(Drift − Calibration Reading) ÷ Cylinder Concentration × 100
Calibration PPM	(Drift − Calibration Reading) ÷ Calibration Reading × 100
Cylinder PPM (default)	(Drift − Cylinder Concentration) ÷ Cylinder Concentration × 100

A value of 0% means the drift reading exactly matched the reference value. Negative values indicate the analyzer is reading lower than expected; positive values indicate higher.

Drift 1 vs Drift 2

Drift 1 is the mid-day (Noon) drift check, taken partway through the inspection shift.
Drift 2 is the end-of-day drift check, taken at the end of the shift.

Not all sessions will have both; either drift may be blank if that check was not performed.

Tips and Common Questions

"Drift columns are blank for some rows." If no mid-day or end-of-day drift was performed for that calibration session, the corresponding Drift columns will be blank. Zero gas rows also never show drift percent values.
"There are multiple rows per analyzer per date." Each cylinder used in the morning calibration produces one row. A typical session includes a zero gas and several span gases.
"Ext Probe = Yes but the morning calibration used Standard." Ext Probe reflects whether the calibration activity used an extension probe. A session can include both Standard and Extension probe readings on different gas cylinders.
"The Pct. sign is negative — does that mean it failed?" A negative percent deviation means the analyzer is reading lower than expected. Whether this is a pass or fail depends on your site's drift limit (typically ±10% or ±20% depending on the regulation). Check the Pass column for the actual pass/fail result.
"This report only shows Standard drift — where is VVa drift?" Analyzers drifted using the VVa method appear in the VVa Drift or VVa Drift – Form 2 reports instead.

Sample Output (click here for PDF sample report)

Report run for Example Facility, Start Date: 9/22/2022, End Date: 9/22/2022, Analyzers: phx42-3536, phx42-3584, phx42-3590, phx42-3599, and phx42-5389.

What the rows illustrate:

CT-24077 (zero gas) — Zero gas row; no drift percent shown. Drift1/Drift2 columns are blank.
phx42-3536 (CT8327) — Drift 1 at 1:41 PM showing −3.98%; Drift 2 at 4:36 PM showing −0.31%. Both pass. The analyzer is drifting lower throughout the day but remains within limits.
phx42-3536 (T7790071) — Smaller drift values than before across both mid-day and end-of-day checks; well within acceptable limits.

Output Format

One row per gas cylinder per morning calibration session. Drift 1 and Drift 2 readings appear as additional columns in the same row. Suitable for on-screen viewing, PDF, and Excel export.

Related Reports

VVa Drift — drift checks performed using the VVa method (three readings per drift event, NSPS (New Source Performance Standards) VVa and Consent Decree compliance columns).
VVa Drift – Form 2 — simplified VVa drift format with Cal Note column.
Daily Calibration — the morning calibration readings without the drift check columns.