testo 915i

The Phone Is the Display

This is the design decision the whole instrument follows from, and it’s worth understanding before comparing it to a conventional thermometer.

The testo 915i has no screen. It connects automatically over Bluetooth to a phone or tablet running the free testo Smart App, and the app becomes the display. Removing the screen and keypad keeps the instrument small enough to fit where a handheld meter can’t.

It also changes where the reading appears. With a conventional probe, the reading is at the probe, so someone has to see it from wherever the probe has been pushed. Here, the reading is on the phone, so the probe can go somewhere you can’t see, and the number still arrives.

Any Type K Probe, Not Only Testo Ones

The handle works with all Testo and other common Type K thermocouple probes. With other Type K probes, the handle measures from -60 to +1,000°C.

That matters more than it sounds. Many instrument manufacturers tie you to their own probe range, so a specialist probe you already own becomes useless. The 915i takes what you have, so an existing probe collection keeps working, and an unusual requirement can be met from any source.

A locking mechanism in the handle holds the four standard testo 915i probes securely, rather than relying on a friction fit. That’s the difference between a probe staying put and one pulling out as you withdraw it from a duct.

Four Probes, Four Jobs

All four are Type K, Class 1. The testo 915i comes with a single probe, or as a kit with the handle and the air, immersion and surface probes in a Smart Case.

The Flexible Probe Solves a Specific Problem

It’s worth calling out, because it’s often the reason people choose this version.

The flexible probe is 800 mm long and thin enough to pass through a drill hole, a gap or a door seal. So the temperature inside a closed space can be measured without opening it.

That covers cold room and freezer door seal checks, cabinet and enclosure interiors, and any situation where opening the space to take a measurement changes the thing being measured. A rigid probe can’t do it.

One Hundred Metres of Range

Bluetooth reaches up to 100 metres, which turns a convenience into a capability.

A probe can be left in position in a duct, a cool room or a plant space, and the reading taken from outside it. On a measurement that needs time to settle, the technician doesn’t need to stand next to it waiting. In a space that’s uncomfortable or awkward to be in, it means not being in there at all.

It Extends Other Instruments

The 915i also connects to Testo measuring instruments, such as the testo 400 and testo 550s.

That adds a wireless temperature channel to an instrument already measuring something else. On an HVAC commissioning job, that means one instrument reading air velocity and CO2, while the 915i reads a temperature it can’t reach.

Documentation

The Smart App displays readings and presents temperature curves graphically, rather than as a single number. Measurement reports can be created in the app, with photos and comments added, and sent as PDF or CSV files.

The graphs are the part worth having. A single number tells you the temperature now. A curve tells you whether it’s stable, rising or cycling, which is usually the real question on a commissioning or fault finding visit.

The handle and probe are calibrated together as a system, ex works, with system accuracy from ±1.0°C, depending on the probe and range.

One Limitation Worth Knowing

The 915i is a general purpose instrument. It has no hazardous area certification, and it needs a phone or tablet to display anything.

Both matter for some of the work our customers do. In a classified area, neither an uncertified instrument nor a phone is permitted, so this isn’t the tool for a temperature measurement inside a Zone 1 area. And on a site where phones are restricted, the display requirement is a practical obstacle.

For plant rooms, workshops, HVAC systems, cool rooms and general industrial work, it’s straightforward. For hazardous areas, talk to us about a certified alternative.

Where It’s Used

HVAC commissioning and fault finding. Duct and air outlet temperature measurement. Flow and return temperature on heating and cooling systems. Cool room and freezer checks, including door seals. Food processing and handling. Laboratory work. Plant room surveys. General maintenance and service work.