Quick answer
HACCP instruments must be suitable for the measurement and kept reliable through appropriate checks, calibration and maintenance. Set the method and interval from the instrument, use, conditions, risk and relevant requirements. If an instrument is inaccurate, assess the food decisions made with it as well as repairing or replacing the device.
Choose an instrument fit for the decision
MyHACCP monitoring guidance identifies calibrated, correctly working equipment, including meters for pH and water activity. Check the range, resolution, accuracy, response and method needed to distinguish the relevant control condition.
A device displaying several decimal places is not necessarily accurate enough or suitable for the product. Probe selection, sample preparation, loading, sensor position and environmental conditions can influence what a reading means.
Distinguish checks, calibration and adjustment
A routine check asks whether performance remains acceptable against a suitable reference or method. Calibration establishes the relationship between an instrument’s indication and reference values under defined conditions. Adjustment changes the instrument; it is not the same as documenting its prior performance.
NPL’s mass/weight guidance explains the importance of assessing balances under relevant use conditions and considering performance factors. Apply competent measurement advice to the actual instrument rather than treating a calibration sticker as the whole assessment.
Plan instrument-specific arrangements
| Instrument | What the plan should address |
|---|---|
| pH meter | Suitable electrode, sample method, reference buffers, temperature conditions and manufacturer instructions. |
| Scale or balance | Relevant load/range, placement, reference weights and performance in actual use. |
| Data logger | Sensor range, comparison evidence, placement, time settings and data interpretation. |
| Other process meter | A suitable reference, method, acceptance criteria and competent support. |
This is a planning checklist, not a universal calibration procedure. Do not prescribe identical intervals or tolerances for every device.
Retain meaningful evidence and respond to failure
Record device identity, method, reference, date, findings, acceptance criteria, adjustments and authorisation as relevant. Check that a calibration certificate covers the instrument and measurement range actually used; seek competent interpretation where uncertainty matters to a safety decision.
Illustrative example: a meter check finds a significant offset. Remove or control the device, investigate when reliability may have changed and assess affected records and food decisions. A newly acceptable reading after adjustment does not retrospectively validate earlier results.
Assign ownership and review changes
Identify who checks, maintains and authorises devices and how cover or alternatives work. Review after damage, repair, unstable readings or changed use conditions. Train staff to report implausible results rather than repeatedly measuring until a preferred number appears.
Use the existing temperature-check guide for basic practical temperature context and the HACCP review guide for evidence. Keep specialist calibration methods with competent instructions.
Next steps
- Select a device and method suited to the control decision.
- Define relevant checks/calibration, criteria and ownership.
- Retain evidence and investigate out-of-tolerance findings.
- Assess affected food decisions and verify reliability before reuse.
Read the official practical guidance — Use the current source alongside the procedures for your own business.