Put quotes side by side on the same scope: what is included in the sample system, what range and accuracy basis (span or reading), what response time and at what flow, certificates and documents, calibration gas and spares, commissioning and support, and what is excluded. Differences in scope explain most price differences. Ask each supplier the same questions in writing.
- List the items to compare in every quote
- Spot exclusions and hidden extras
- Ask the questions that expose differences
The comparison table
| Item | Questions |
|---|---|
| Scope | Analyser only, or probe, line, conditioner, filters, regulators, enclosure, cabling? |
| Measurement | Gas, range and minimum range, and the range proposed against your operating value |
| Accuracy | Percent of span or of reading? Under what conditions? Drift per period? |
| Response | T90 at what flow, and the sample line lag: Response time, T90 and sample lag in gas analysis |
| Sample limits | What sample the analyser accepts and what yours is: What samples an analyser cannot take: know the limits |
| Site | Area classification certificate, enclosure rating, ambient limits |
| Outputs | 4-20 mA, relays, Modbus, fault behaviour |
| Calibration | Method, gas needed, auto-calibration, who supplies the gas |
| Documents | Datasheets, certificates, drawings, register map, manuals |
| Commissioning and training | Included, and by whom |
| Spares and service | Recommended spares, sensor life, service response |
| Exclusions and assumptions | What the quote relies on that you must provide |
Traps
- Different range for the same price: a wider range gives worse resolution for a purity decision.
- Accuracy on different bases: percent of span versus percent of reading.
- Missing conditioning: the analyser works on a clean sample you do not have.
- Certificates by assumption: the analyser is certified but the sample arrangement is not.
- No support statement, left until after the order.
Ask the same questions of everyone
- Is the quote for a complete working measurement on my sample?
- What do I have to supply?
- What is excluded?
- What is the first year's consumable and calibration cost?
- What happens when I call with a problem?
Reduce each quote to a one-page list of scope, performance and exclusions before comparing prices.
Cost of ownership
Add the running costs from Total cost of ownership of a gas analyser and weigh them with accuracy and support: What accuracy do you really need from a gas analyser. A quote that states its limits, including what an analyser cannot take, deserves some weight: Questions to ask a gas analyser supplier before you buy.
- Compare on the same scope; scope explains most price differences.
- Check range, accuracy basis, response and sample limits.
- Look for exclusions, assumptions and missing conditioning.
- Ask everyone the same written questions.
Check your understanding
Answer in your head or on paper first, then open the answer. Recalling an answer teaches more than rereading.
Why can the same analyser be quoted at very different prices?
One quote may include the sample system and commissioning and the other not.
Name two accuracy bases that look similar but differ.
Percent of span and percent of reading.
What is a common exclusion to watch for?
Sample conditioning, or installation and commissioning.
Key terms
Frequently asked questions
How do I compare gas analyser quotes?
On the same scope and basis, with exclusions and running costs listed.
What should every quote include?
Scope, performance, certificates, documents, calibration, commissioning and support.
Is a lower price a warning sign?
Check what is missing.
Can you quote against my specification?
Yes. Send it with the application data sheet.
