Image note: The representative website photograph shows a luminaire, not an RTD, thermocouple or temperature-measurement assembly. Verify exact model marking, certificate scope and current documentation before interpreting any product claim.
RTD vs thermocouple: keep the measurement and Ex questions separate
The twelve questions below help organise a temperature-sensor enquiry. They do not select a device for a process or provide installation instructions. Define the measurement task first, then have the responsible professionals review the offered configuration and its separate explosion-protection evidence.
1. What is the practical difference between the two principles?
For a platinum resistance thermometer, NIST describes how the metal's electrical resistance changes with temperature. Its PRT explanation connects that electrical behaviour to the measurement electronics. NIST's thermocouple explanation instead describes thermoelectric voltages and a reference-temperature relationship.
The buying consequence is simple: the receiving instrument must suit the specified sensor arrangement. Similar-looking probes do not establish equivalent signals or compatible measurement electronics.
2. Does an RTD label identify a complete specification?
No. Ask for the element material, exact type and the manufacturer's complete ordering reference. The current IEC 60751:2022 catalogue covers industrial platinum resistance thermometers and platinum temperature sensors, including their resistance/temperature relationship. It does not describe every possible RTD material or approve a particular probe.
The catalogue identifies Edition 3.0, published January 27, 2022. Keep the offered device's own stated reference and controlled documentation alongside that general standard information.
3. Is a thermocouple type letter enough to place an order?
No. A type designation is one field, not the complete supplied construction. The official IEC 60584-1:2013 record addresses reference EMF functions and tolerances for designated thermocouple types. It identifies Edition 3.0, published August 28, 2013.
Ask the supplier to identify the complete probe, connection arrangement and associated measurement equipment being offered. A familiar letter does not establish mechanical suitability, calibration evidence or hazardous-area approval for the assembly.
4. Is the measured temperature the same as the Ex temperature class?
No. The process temperature being measured, the sensor's documented operating conditions and the equipment's Ex temperature marking answer different questions. State each separately in the enquiry so an answer about one cannot be mistaken for acceptance of the others.
The temperature-class and ambient-temperature guide explains the separate Ex fields. This FAQ does not derive a permitted process temperature from a T-class or infer a T-class from a sensor's measurement range.
5. What should I say about the measurement location?
Describe what needs to be measured, where the sensing arrangement will be used and the operating situations that matter to the project. Distinguish a desired measurement task from a proposed product specification. Include available process and environmental information without filling unknown fields with assumed values.
Ask the responsible reviewer which additional information is needed. This article does not prescribe an insertion depth, a mounting position or a process penetration.
6. Can probes with matching dimensions be substituted?
Not on dimensions alone. Request a comparison of the complete ordering references, sensor principle, stated performance conditions, mechanical construction and associated documents. Record any difference for the responsible reviewer rather than declaring the devices interchangeable from their outline drawings.
If an existing installation is involved, preserve the original identity and instructions. This purchasing comparison does not authorise removal, replacement, wiring changes or alteration of a protective enclosure.
7. Should the readout or transmitter be identified in the enquiry?
Yes. Identify whether the offer includes the sensor only, a sensor with a transmitter, or a larger measurement arrangement. Ask the supplier to explain the documented relationship between the proposed sensing element and the receiving equipment.
Do not assume that two devices described as temperature inputs accept the same sensor. Let the responsible designer verify the controlled interface information; this FAQ gives no terminal mapping, compensation circuit or connection procedure.
8. Which accuracy and response claims should I compare?
Compare claims for the actual offered configuration under the conditions the supplier states. Ask what each performance figure describes and whether it concerns an element, probe or complete measurement arrangement. Preserve limitations and the basis of the claim.
There is no universal accuracy or response-time winner established here. If a project requires a particular result, the responsible reviewer must determine whether the supplied evidence answers that requirement rather than selecting a sensor family by reputation.
9. What does a calibration document need to identify?
Ask which actual item or arrangement was calibrated and how its identifier relates to the offer. Retain the report reference, issue date, stated conditions and results for review. If the document concerns a different item, ask the supplier to explain its relevance instead of silently carrying the result across.
A calibration record is measurement evidence, not an Ex certificate. This FAQ specifies no universal calibration interval or acceptance tolerance.
10. Does a passive sensor automatically qualify as simple apparatus?
No such conclusion follows from the family name or the absence of a separate power supply in a description. The responsible specialist must consider the actual construction and its place in the intended system using the applicable requirements and documentation.
The intrinsic-safety simple-apparatus guide addresses that separate evidence question. This article does not assign intrinsic safety, approve associated equipment or authorise an undocumented sensor connection.
11. What establishes the separate hazardous-area claim?
Review the exact legal manufacturer, model and options, complete marking, applicable conformity records, scope, conditions and instructions. The proposed configuration must be identifiable in the evidence relevant to its destination and application.
Use the certificate-verification guide for that separate review. A measurement standard, type letter, calibration report or photograph does not substitute for it. Keep unresolved product and document differences visible before an acceptance decision.
12. What should purchasing retain after the review?
Retain the measurement brief, complete supplied-item references, performance documents, calibration evidence where relevant, separate Ex records and the responsible review outcome. Keep supplier clarifications and document revisions with the final offer.
If the sensing element, electronics, mounting arrangement or operating conditions change, return the difference for review rather than assuming the earlier answer still applies. This is an editorial document-control workflow, not a mandatory checklist reproduced from either sensor standard.
Current MMAIATEX certification status
MMAIATEX is the public brand of MMAIATEX Explosion-proof Technology (Zhejiang) Co., Ltd. On the review date, its About page states that ATEX, IECEx and CCC certification is in progress. This is an attributed website statement, not independent certificate verification. No available or certified RTD, thermocouple or complete temperature-measurement model is announced here.
Safety and legal disclaimer
These answers are general purchasing information, not measurement-system design, calibration instructions, hazardous-area approval or permission to install or modify equipment. Competent professionals must assess current requirements, exact product records and the actual application. Do not perform wiring, process modifications or hazardous-location tests using this FAQ.
Contact MMAIATEX
Send the measurement task, proposed sensor and readout identities, available conditions and the specific document question. Identify missing information without implying a product capability or approval that has not been established.