Calibrating and Maintaining a Tiger PID Detector: Bump Test, Lamp Cleaning, Electrode Replacement

A PID detector is an instrument whose readings decide whether a person may work in a zone. So the question "is it reading correctly?" must have a documented answer every day. Photoionisation sensors are sensitive to lamp and electrode contamination, and an instrument with a dirty lamp may show a calm zero where the concentration is already hazardous.

Below is a practical maintenance routine for Tiger and other Ion Science PIDs: what to do before every shift, monthly and annually.

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Three different procedures that are often confused

Procedure	What it checks	How	When
Bump test	The instrument responds to gas and alarms	Brief exposure to a known concentration, no adjustment	Before every use
Calibration	Readings match actual concentration	Zero with clean air and span with reference gas	After a failed bump test, per schedule, after maintenance
Verification	Metrological conformity to the approved instrument type	At an accredited laboratory	At the interval stated on the certificate

A bump test does not replace calibration, and calibration does not replace verification. They are three levels of control with different frequency and purpose.

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Bump test: before every shift

Purpose: confirm the sensor is alive, the lamp is on, the pump draws a sample and the alarm works.

Steps:

1. Switch the instrument on in clean air and wait until it is ready.
2. Apply calibration gas (usually 100 ppm isobutylene) through the adaptor.
3. Confirm the reading rises within tolerance (for example ±20% of nominal; check your corporate procedure) and the alarm triggers.
4. Record the result.

If it fails: the instrument is not used until calibrated. If calibration also fails: clean the lamp, replace the filter, then calibrate again.

The typical cause of a failed bump test is not the sensor but a blocked inlet filter or a kinked sample hose: gas simply does not reach the sensor.

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Calibration: zero and span

Zero. Apply clean air, either from a zero air cylinder or through a carbon filter. Zeroing in "clean workshop air" without a filter is a common mistake: if the workshop background is 0.5 ppm, that background becomes the new zero and all subsequent readings will be low.

Span. Apply reference gas: isobutylene of known concentration from a certified cylinder. Use the flow rate specified in the instrument manual, through a regulator and adaptor.

When to calibrate:

• after a failed bump test;
• after lamp cleaning or replacement of the electrode stack or filter;
• after exposure to high concentrations (the sensor may be saturated or contaminated);
• per site schedule, more often under heavy use;
• when changing the lamp.

Tip: calibration gas has an expiry date; check it on the cylinder certificate. An expired cylinder gives a false calibration.

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Lamp cleaning and electrode replacement

Why the lamp gets dirty

The PID UV lamp has a window through which radiation passes. Over time a film forms on it: photolysis products of organic substances, dust, condensate. The film absorbs UV and sensitivity drops. This happens especially fast when working at high concentrations and in dusty, humid environments.

Signs of a dirty lamp:

• calibration passes but sensitivity drops quickly afterwards;
• the instrument needs calibration more and more often;
• unstable readings on zero air.

How to clean it

Clean the lamp window with the polishing compound from the manufacturer's lamp cleaning kit using a gentle circular motion, then remove residue. Do not touch the window with your fingers or use solvents or abrasives not supplied in the kit. Calibrate after cleaning and reassembly.

Electrode stack

Sensor electrodes also get dirty and wear over time. Fence Electrode technology in Ion Science instruments reduces the effect of humidity and contamination but does not eliminate it. If lamp cleaning does not restore stability, replace the electrode stack. It is a consumable with a finite life.

Filters

The inlet filter protects the sensor from dust and droplets. Replace it per schedule and immediately when visibly dirty. Running without a filter "for faster response" is a direct route to a contaminated sensor.

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Maintenance schedule: summary table

Task	Frequency	Who
Visual check, battery check	Before every use	User
Bump test	Before every use	User
Zero and span calibration	Per site schedule and after maintenance	Trained user / instrumentation team
Inlet filter replacement	When dirty, at least per schedule	Trained user
Lamp cleaning	When signs of contamination appear, after high-concentration work	Instrumentation team
Electrode stack replacement	When worn	Instrumentation team / service
Verification	At the verification interval	Accredited laboratory

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Records for audits

If an incident occurs on site, the first question from the investigation is "was the instrument working?" The answer must be documented:

• a bump test log with date, instrument number, result and name;
• a calibration log with cylinder number and expiry date;
• a maintenance log: lamp cleaning, filter and electrode replacements;
• a valid verification certificate.

Tiger instruments store measurement history, and Ion Science software allows data to be downloaded. Use this, not just a paper log.

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Verification in Kazakhstan

Gas detectors used for safety monitoring fall within the scope of state regulation of measurement uniformity and are subject to verification. An imported instrument needs an approved measuring instrument type in the Kazakhstan register. When purchasing, ask the supplier about the type approval certificate and the initial verification procedure. More on organising verification in the article on verification and calibration of measuring instruments.

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In frost and in heat

• Frost. Batteries lose capacity; keep the instrument warm and bring it out into the cold just before work. When moving from cold to warm, let the instrument warm up while still closed, otherwise condensation forms inside.
• Heat and dust. Replace the filter more often and do not leave the instrument in direct sunlight in a vehicle.
• High humidity. Fence Electrode reduces the effect of humidity, but a bump test is especially important in these conditions.

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Summary

A reliable PID detector is not only a good instrument but also discipline: a bump test before every shift, calibration per schedule, a clean lamp, a fresh filter, valid verification and records you can produce. Without this, even the best instrument can show a safe zero where it is not safe to work.

KEG TRK supplies Ion Science instruments, calibration gases and consumables, and advises on organising maintenance and verification. Instrument selection is covered in the article on choosing a PID detector.