Beginner questions on temperature measurement - Sensors

Hi,

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We are working on a temperature measurement project. The goal is to have fun, but it might turn out to be practical.

The 'target' to be measured will be grape buds and grape leaves experiencing frost. Temperature readings will be taken outdoors just before dawn, when air temps will be around 0 C (+/- 5 C). The lowest expected surface temperature will be around -5 C. The results will then be compared to plant tissue damage (or lack of damage) observed over the next few days. Eventually, we would like to put 50-100 sensors in the vineyard and hook them up with wireless units.

Here is our prototype. It is using two thermistors. The '3 wire' digital thermistor is visible in the bottom right. Two wire thermistor leads can be seen in the upper left.

We have logged data at 5 second intervals to both a file, and command-line window of a Windows-XP computer. The results looks accurate.

The first problem is calibration. For a growing grape bud, the difference between -2 C and -4 C can be life or death, so +/- 0.5 C accuracy is critical. It seems an ice water bath will provide a good 0 C 'known' temperature value for calibration in the field. Platnium sensors seem the best for stable, high resolution sensors. For now, we are Murata Electronics NXFT15XH103FA2B100 (2 wire), and Maxim Integrated DS18B20+ sensors. We have 3 to 5 sensors of each type. It isn't clear how to water-proof them for testing the 'ice bath' procedure.

Second, we would like to have an accurate hand-held unit for spot checks. When we look at handheld units for sale, we don't understand enough to know what we are looking at. Apparently, a PT-100 RTD is recommended, but PT-100 seems to be a generic title for a vast number of sensors, none of which are called PT100. So, if we get a platinum PT100 sensor for surface readings in the 0 C range (high quality), it isn't clear what hand-held device we need for data-logging and real-time display. Further it seems we can hook a PT100 sensor directly to our Arduino and (if it can operate at 0 C) take our measurements with the prototype set-up. I'm not sure we encounter the water-proofing issue with a platinum PT-100 RTD. I can't make sense of the parts listings.

Any suggestions would be appreciated.

JoeBob

JoeBob:
it might turn out to be practical.

It is using two thermistors. The '3 wire' digital thermistor is visible in the bottom right. T

The first problem is calibration.
we are Murata Electronics NXFT15XH103FA2B100 (2 wire),

and Maxim Integrated DS18B20+ sensors.

a PT-100 RTD is recommended, but PT-100 seems to be a generic title for a vast number of sensors,

I think there are some you haven't mentioned but I submit you would be better off attending to one type of sensor.

Even though you already have thermistors working, I would suggest you go for the DS18B20. They are cheap, need no calibration, accurate to a fraction of a degree, simple to install using a one-wire sytem, and are available in a weatherproof package. They are also popular and well-supported in this forum.

Your second problem is far from clear but, whatever it is, an Arduino can handle it. Quite possibly the same Arduino.

Hello everyone,

I have tested aqara and sonoff temperature sensors and none of the above have satisfied me.

Aqara keep disconnecting frequently so it is unreliable.

And sonoff temperature sensor are reporting way to slow (I believe once per 2 hours) which make it impractical in home automation, as in 2 hours the temperature can change drastically.

I have used all 3 drivers (Mariano, STE-roadDOG and official smart things driver)

Even tho I set the reports at 5 minutes, sometimes it works but most of the time don’t.

Anyhow, I need some temperature sensors (ZigBee/zwave) to be small and to work nice with smart things (frequently updating it’s temperature, preferably every minute)

Any recommendations?

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I believe the stock driver configures them with a reportable change of 0.5 C, with a minimum of ten seconds between reports, and a maximum of two hours. That is consistent with what I see on my devices.

Although the 0.5 C seems a little crude the accuracy of the device is +/- 0.2 C (which is fairly typical) so it is a reasonable and realistic choice.

Most batterypowered sensors will only report a change in state above a predefined delta, in order to prolong battery life. And a typical reporting period for a battery power temperature sensor is once every 15 minutes, which is considered sufficient for heating/cooling room control. If you start going much more often than that, you risk very short battery life.

The alternative is a Mainspowered sensor, which can report frequently, certainly once a minute. Is that an option for you?

There is another factor, which is the act of reporting in itself can raise the temperature around the sensor. For that reason, you will typically get the most frequent reporting from a device which uses an attached probe sensor, so that the sensor is at least a couple of centimeters away from the radio.

For example, Shelley recommends using a DS B temperature probe attached to one of their relays if you need reporting quicker than every 10 minutes.

Here’s their FAQ:

So there are some options, but not in your typical self contained battery operated sensor.

With Mariano’s driver you can set the reporting interval to every 5 minutes with a minimum temperature change of 0.1°.

The cheap Tuya sensors with no LCD display work with Mariano’s driver. The ones that use AAA batteries get better battery life than those using coin batteries.

The ones with LCD displays don’t work with Mariano’s driver. You need to use the “Personal Tuya Devices” driver which doesn’t allow you to set reporting interval or temperature.

I like the Sonoff SNZB02. They are fairly accurate/linear (although the humidity on most is about 6% off, I adjust with driver offset). They are usually about $10-$12 on ebay. I would get them from Sonoff direct. I use them on SmartThings and Hubitat both.

On SmartThings, the STE-RoadDog driver for the SNZB02 works great. It allows for the reporting interval to be changed to between 5 and 120 minutes at minimum.

Hi @Kowalski

The sonoff SNZB02 sensor works very well for me, I have used it as a thermostat for two winters, reporting changes of 0.1°c and the battery still reports 100%.

These devices do not always accept reporting configuration changes when asleep.

It is best to configure during installation.

The events that are seen in the app never report repeated temperature values, although the device sends them and the driver emits the event.
That is why you can see events in the history every 5 minutes or every 2 hours for example, always informed of a change in temperature.

Look at the temperature graph in the app and you will see reports every 5 minutes, even if they are identical temperatures

My driver configures the device with minimum interval, 30 sec, maximum 300 sec and reportable changes of 0.1°c so that it can be used as a thermostat.

If you want to change the reports you can do it in preferences, but not all devices accept them easily.
The zigbee Smartthings Samjin (Aeotec) movement, multifunction, button, are fantastic at accepting configuration changes.

Using the CLI you can check if the device replies SUCCESS when the new configuration is sent.

Note! when you change from one driver to another, as in the stock drivers, the device configuration is not executed and it keeps the configuration it had in the previous driver.

My driver does do the configuration, but not all devices accept it outside of pairing mode and a driver change doesn’t wake up the device if it’s asleep.

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