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Temperature probe commissioning and two-point check record

A free record to commission the temperature probes on a tracking device: put each probe in an ice bath and a second bath next to a reference thermometer, work out the correction, and prove it at a third point.

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  • Ice point and a second point
  • Gain, offset and residual
  • Reference certificate date check
How the correction works

Two baths, one straight line, one proof

The record turns two pairs of readings into a gain and an offset, then checks them at a third temperature.

Gain = (reference 2 − reference 1) ÷ (probe 2 − probe 1) Offset = reference 1 − gain × probe 1 Corrected reading = gain × reading + offset Offset only = reference 1 − probe 1 (when the device takes a single offset) Residual = corrected check reading − reference 3A straight line through two points. It assumes the probe is close to linear between them, which is why the third point checks it.
Worked example: probe T1, return air
StepValue
Ice bath: reference and probe0.00 / 0.40 °C
Second bath: reference and probe25.00 / 25.60 °C
Errors as found+0.40 / +0.60 °C
Gain = 25.00 ÷ 25.200.9921
Offset = 0.00 − gain × 0.40-0.397 °C
Check point: reference and probe10.00 / 10.50 °C
Corrected check reading10.02 °C
Residual against ± 0.5 °C+0.02 °Ctypical
T1 passes after correction

As found it was 0.6 °C high at 25 °C. With gain and offset, the check point is within 0.02 °C.

+0.02 °C
T4 needs a look before any correction

Its gain is 1.092, outside the ±5% band. A slope that far from 1 points to a faulty probe, a bad joint or the wrong input type.

Check probe

Typical value. The ±0.5 °C tolerance and the 5% gain band are examples: replace them with your contract or standard figures.

What's inside

What's in the probe commissioning record?

Four working sheets and a list sheet. Up to 40 probes per job.

  1. 01

    Job

    Vehicle, device, technician, the reference thermometer with its certificate date, and your tolerance, minimum gap and gain band.

  2. 02

    Probe register

    Probe ID, sensor type, compartment, position, device input, cable route, platform name and photo reference.

  3. 03

    Two-point check

    Errors as found, gain, offset, offset only, the check point, the corrected reading, the residual and Pass or Fail.

  4. 04

    Result

    Probes checked, passed and failed, gains outside the band, and one commissioning result for the job.

Why check a probe before go-live?

A temperature report is only as good as the probe behind it. A probe can be a little off from the factory, a long cable or a poor joint can shift an analog reading, and a probe can sit on the wrong input. A two-point check on the day of installation shows the error, fixes what can be fixed, and records the rest.

The ice bath, done right

  1. Fill an insulated flask with crushed ice made from clean water.
  2. Add just enough cold water to fill the gaps, and stir.
  3. Put the probe and the reference side by side in the middle, not touching the wall.
  4. Wait until both readings are steady, then read the probe value the device reports.

Pure ice and water settle at 0 °C at normal air pressure. The record still uses the reference reading, not an assumed 0.0, so a small bath error does not slip into the correction.

The second point and the check point

Pick a second stable bath at least the minimum gap away, 10 °C in the example, and if you can, close to the range the load will see. Then read a third temperature between the two. If the corrected third reading is inside your tolerance, the line holds. If not, the probe is not linear enough, or the wiring has a problem.

Offset only, or gain and offset?

Some devices and platforms accept a single offset per probe. Others accept a gain too. The record works out both. Enter only what your device accepts, and say which in the Correction applied column.

Limits

The record checks probes against your reference thermometer. It is not a calibration certificate, and it does not show that a vehicle meets a food or medicine transport rule. For the readings over a whole trip, use your temperature log. The tolerance, the minimum gap and the gain band are typical examples.

Related Tracom solution

Probes that read right from day one

Tracom designs its devices to take temperature probes and report their readings with the position. Which probe types, how many inputs and which correction a model accepts depends on the model and its configuration. Ask us before you fit a reefer fleet.

  • Reefer sensor plan to plan the probes, door contacts and humidity sensors for each body.
  • MKT calculator to read a log once the probes are in service.
  • I/O mapping sheet to record which input each probe uses.
  • Alert test script to test the temperature alarm after commissioning.
Questions

Probe commissioning questions, answered

Fitting a reefer fleet? Talk to Tracom.

Why two points and not just the ice bath?

One point gives you the offset at 0 °C only. A probe with a slope error reads right at 0 °C and wrong at 25 °C. The second point finds the slope, and the third proves it.

Which reference thermometer should I use?

One with a calibration certificate that is valid on the test day, and better accuracy than the tolerance you check against. The record flags an expired certificate.

What tolerance should I use?

The one in your customer contract or your own standard. The file uses ±0.5 °C as a typical example only.

What does a gain outside the band mean?

Usually not a calibration issue. Check the probe type against the input setting, the joints and the cable, and swap the probe before you correct it.

Is this a calibration certificate?

No. It is a commissioning record of a check against your reference. A calibration certificate comes from a calibration lab.

What does Tracom do beyond the template?

Tracom makes the devices the probes connect to, and can tell you which probe types and corrections a model accepts. The record works with any device. It does not certify a probe, a vehicle or a cold chain.

Next step

Fitting probes on a reefer fleet?

Tell us the trailers and the loads. We will help you plan the probes and the inputs.

Contact Us Get the record
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