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Step one: define the safe range and the sensor spot
Start by writing the range the unit must hold. For a walk-in cooler storing dairy and produce, a common internal target is roughly one to four degrees Celsius, but confirm the figure against your local food safety rules and product guidance. Then choose the probe position: away from the door, away from the evaporator fan and near the product, not the wall. A reading taken beside the compressor will mislead you. Mark the spot, note it in your log and keep it consistent so every future reading is comparable with the last.
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Step two: set thresholds with a delay
Set a warning level slightly inside your limit and a critical level at the limit itself. In the cooler example, a warning might trigger at four degrees and a critical alert at five. Add a delay of fifteen to thirty minutes so that door openings during deliveries do not wake anyone at night. Also add an alert for lost signal, because a silent sensor can look like a healthy one. Review the first week of readings, then tighten or relax the settings based on actual patterns, not guesses made before the unit has been observed.
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Step three: assign response and test the chain
An alert is only useful if a named person acts on it. List who receives the warning, who receives the critical message and who steps in if the first person does not acknowledge within a set time. For the cooler, that might be the shift lead, then the manager, then a refrigeration contractor. Write down the first actions: check the door seal, confirm the reading with a handheld thermometer, move high-risk stock if needed. Finally, trigger a test alert, confirm delivery on every phone and record the date so the routine is checked regularly.