Frequently Asked Questions:
Dial Thermometers

The maximum operating temperature is 500F (260C). The minimum operating temperature is -50F (-45C).

Choose a dial thermometer when you need a cost-effective, durable, and reliable instrument that does not require external power. They are ideal for applications where continuous local monitoring is needed and slightly lower precision (typically ±1% or 2% of span) is acceptable.

Adjustable angle models offer flexibility for hard-to-reach installations, allowing the case to be rotated 360° and the stem to be angled up to 180° for optimal visibility. Back connection models are ideal for panel mounting or when the installation point is directly behind the dial face.

Yes, Tel-Tru Dial Thermometers are hermetically sealed. This design prevents moisture and debris from entering the internal mechanism, which is critical for preventing fogging, extending the instrument’s lifespan, and ensuring reliable performance in humid or washdown environments.

The critical sensing area (tip) of a bimetal thermometer must be fully immersed in the medium being measured. Tel-Tru recommends a minimum immersion length of 2.5 inches (63.5 mm) for most applications to prevent ambient temperature from affecting the reading and ensure measurement accuracy.

High-quality bimetal dial thermometers are designed with an external reset nut or calibration adjustment screw. Tel-Tru models allow for easy adjustment in the field to maintain peak performance. For traceability, always verify the recalibration against a known standard like a certified Check-Set Calibrator.

Any distance at which the thermometer case is not exposed to heat beyond 200F.

The paint on the dial is not rated for high heat. Exposure to high heat may cause the paint to discolor or crack.

The thermometer’s hermetic seal creates a pocket of air inside the thermometer. When heated, this pocket of air creates pressure which can damage the thermometer.

Yes, these certificates must be requested on your purchase order with the thermometers, pressure gauges, thermowell, etc. The certificates are sold seperately and are on our website.

Yes. Tel-Tru can manufacture custom stem lengths up to 120″ for dial thermometers.

No. Glycerine is not an option for filling dial thermometers because it is too viscous and it will not tolerate high temperatures.

Yes, polycarbonate plastic is standard on silicone thermometers. Shatterproof glass is available upon request.

Both the polycarbonate plastic and the acrylic plastic materials are UV stabalized materials, which means the yellowing is delayed but will still happen over a long period of time.

Tel-Tru products do not carry the “N Stamp”, but our products are used in the non-nuclear system or side of nuclear power plants. To our knowledge, there are no manufacturers of dial thermometers who have “N Stamp” approval.

Standard lead time is 5 business days from receipt of order and depends on quantity.

Yes. For the most accurate temperature reading the stem must be immersed into the medium at least 2-3″. Unique to all Tel-Tru Dial thermometers is a groove on the stem that equals the minimum immersion depth so you won”t have to measure.

The dial is not flat. There is an outer ring that is raised to the same height as the pointer which allows the pointer position to be read more accurately from various angles.

dial thermometers are not certified for pressure applications. It is standard industry recommendation that anytime pressure is an issue a thermowell should be used for safety reasons.

The pointed stem is the result of a high quality manufacturing process for sealing the stem tip. We do offer blunt tip options as well.

304SS is the standard material for the case, bezel and wetted parts. 316 stainless steel parts are available on some models as an option.

See our Dial Thermometer catalog; if you do not see the temperature range desired please send us an RFQ and we will determine if we can offer.

Custom dial configurations are available. Contact our factory with your requirements. Please contact us at 877-632-3827/585-302-2807 or contact us via the web.

Stem lengths for thermometers with threaded connections are measured from the top of the thread to the tip of the stem. Non threaded thermometers are measured from the back of the case to the tip of the stem. See our dial Thermometer catalog.

No, you will destroy the thermometer. The dial coil assembly in the lower 2″ of the stem is the operating mechanism.

Stem length depends on the model, temperature range and the application. If you do not see the stem length desired please send us an RFQ and we will determine if we can offer.

Yes, Tel-Tru dial thermometers are hermetically sealed per ASME B40.3 test.

+/- 1% full span per ASME B40.3 Grade A.

The Tel-Tru Check-Set Calibrator allows you to verify the accuracy of dial thermometers and digital probes of all sizes. Our multi hole units fit probes up to .250″, .125″, .187″ and .375″ diameter. The Check-Set Calibrator allows accurate verification of thermometer accuracy at the temperature point critical to the users actual application. For more information visit Check-Set Calibrators.

To recalibrate Tel-Tru Dial Thermometers first read the information on Testing the Accuracy of your Thermometer. Also you may refer to our Pocket/Laboratory/Testing/Spot Checking or Industrial dial Thermometers product manuals. The thermometer must have a recal/reset feature (Ex: GT300R, AA375R, LT225R, etc) Or see our manuals: https://www.teltru.com/wp-content/uploads/01204003.pdf or https://www.teltru.com/wp-content/uploads/01204001.pdf