Why an air temperature sensor isn't enough, and what a glycerin bottle is
An air temperature sensor measures the air in the refrigerated space, not the stock. Air reacts within seconds every time the door opens, while the product itself reacts slowly. A sensor placed in a sealed bottle filled with glycerin gains thermal mass that mimics the product, so it shows what is really happening to your stock.
The problem every business owner knows, even without a name for it
A monitoring system that measures air sends an alert every time someone opens the door for three minutes to take out a crate. In the first week, you check every alert. By the third week, you stop looking. By the second month, the alerts are filed away in a folder on your phone.
And that is the moment the system stops protecting your business — not because it broke, but because nobody believes it anymore. When the real alert comes, it looks exactly like everything before it.
The common fix in the field is to push the threshold out: instead of alerting at 4°C, alert at 8°C. It really does cut false alarms, and to the same degree it delays the real alert — until the product has already reached a temperature there's no coming back from.
Thermal mass, in one sentence
Air changes temperature quickly. A block of frozen meat changes temperature slowly. That difference is called thermal mass, and every accurate refrigeration measurement starts with it.
A glycerin bottle is a sealed, liquid-filled bottle that the sensor sits inside. The liquid gives the sensor thermal mass, so it warms and cools at the pace of the product rather than the pace of the air. A three-minute door opening barely moves it. A unit that has stopped cooling does.
The practical result: the same alert threshold that produces a steady stream of false alarms with an air sensor produces a few genuine alerts with a product sensor. You don't need to push the threshold out to silence the noise.
Why glycerin and not another liquid
Four reasons, all practical:
Density. Glycerin is a dense liquid, and at the volume used it changes temperature at a rate close to that of the product itself. That is the whole point of the bottle.
Non-flammable. It's a component that sits inside a refrigeration unit for years.
Inexpensive. There's no reason a passive component should drive up the cost of installation.
Easy to clean. If the bottle gets knocked and breaks, whatever spills on the stock is simple to clean up.
The glycerin bottle is installed once. It has no replacement schedule and needs no routine maintenance.
Comparison table
| Air temperature sensor | Product temperature sensor | |
|---|---|---|
| What is measured | The air in the space | A liquid whose thermal mass mimics the product |
| Response to a 3-minute door opening | Jumps immediately | Almost no change |
| Response to a unit that stopped cooling | Fast | Gradual and steady |
| False alarms | Many | Few |
| What the alert tells you | "The air warmed up" | "The stock is at risk" |
| Threshold needed to silence the noise | High, and therefore late | Not needed |
Why product temperature alone isn't enough either
A product sensor solves the noise, but raises a new question: if the product reacts slowly, won't the alert come too late?
The answer is that the three measurements in basic monitoring work together, not each on its own:
Product temperature tells you whether the stock is actually at risk.
Evaporator temperature tells you whether the unit is cooling. The difference between the air entering the evaporator and the air leaving it is a direct measure of cooling performance, and when the unit stops working, that difference changes before the product warms up.
Door status tells you the cause. A temperature rise while the door is open is an operational event. A temperature rise while the door is closed is a fault.
It's the combination that makes possible the distinction every business owner wants and no air alert provides: between "someone left the door open for ten minutes" and "the unit is failing to cool".
What it looks like at a real customer
An active customer with 8 refrigerators received 4 genuine rising-temperature alerts within two days of installation. All from the same cause: a door left open.
Notice what this story doesn't tell. It isn't about a burned-out compressor or a refrigerant leak. It's about an everyday operational habit the owner didn't know they had — four times in two days, across eight refrigerators. Without measurement, this goes on for years and only comes to light on the day it ends in thrown-out stock.
Technical details worth knowing
Measurement accuracy: ±0.5°C.
Temperature alerts are based on an average of about 10 minutes, by design. This is an extra filtering layer on top of the glycerin's thermal mass.
The default open-door alert threshold is 10 minutes.
NITARTI sets the thresholds at the end of installation, based on the behavior observed in the unit itself rather than a generic value. The values set are recorded in the installation summary the customer receives.
Installation requirements: an existing 230V outlet, Wi-Fi or a network cable, and physical access to the unit. No limitation down to −25°C. The downtime for each unit is communicated in advance.
Questions and answers
A product sensor reacts slowly — doesn't that delay the alert?
No. If the product hasn't warmed up, there's no damage. At the same time, the evaporator sensor shows that the unit has stopped cooling before the product temperature rises, so the alert arrives early and it's accurate.
Can't I just use an air sensor and raise the alert threshold?
You can, and that's exactly what most businesses do. A high threshold reduces false alarms, and to the same degree it delays the real alert. The solution is to change what you measure, not to push the threshold out.
What is a glycerin bottle in temperature measurement?
A sealed, liquid-filled bottle that the sensor sits inside. The liquid provides thermal mass, so the sensor warms and cools at the pace of the product rather than the pace of the air.
Why glycerin and not another liquid?
It's dense, and at the volume used it changes temperature at a rate close to that of the product. It's also non-flammable, inexpensive, and easy to clean up if the bottle gets knocked and breaks.
Does the bottle need replacing or maintenance?
No. It's installed once, and there's no replacement schedule or routine maintenance.
Who sets the alert thresholds?
NITARTI, at the end of installation, based on the behavior of the unit itself. The values set are recorded in the installation summary the customer receives.
Does the system measure defrost cycles?
There's no dedicated defrost measurement — no duration, no frequency and no separate temperature. Defrost cycles are visible in the temperature history chart.
Want to see this on your own equipment?
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