How do I monitor temps above 122 degrees with ISY994i?

[fox7]

My goal is to monitor my solar hot water heater, and to turn on a recirculation pump whenever the water temperature reaches 140 degrees or above, and off if the water temperature falls below 140 degrees.

 

I purchased an INSTEON Wireless Thermostat (2441ZTH) and a Waterproof Temperature Sensor for INSTEON Wireless Thermostat (2433A3).

 

I saw the post by jmed999 showing how to get the Wireless Thermostat to report the external Waterproof Temperature Sensor readings to the ISY (instead of its internal temps).

 

http://forum.universal-devices.com/viewtopic.php?f=26&t=9833&p=74607&hilit=waterproof+temperature+sensor#p74607

 

I've confirmed with the Smarthome INSTEON support line that the external Waterproof Temperature Sensor supports temperatures up to 185 degrees.

 

The problem I'm running into, is that within an ISY program, the ISY994i only supports temperatures up to 122 degrees.

 

Any suggestions on how to get the ISY to monitor temperatures up to 150 degrees or so?

 

If it turns out this isn't possible with this combination of hardware, are there any other INSTEON solutions for monitoring temperatures up to 150 degrees or so?

 

Thanks for any help.

 

Patrick

[Brian H]

Did you disconnect the internal sensor and solder the external probe in its place? As shown it the thread you mentioned.

If you did. You will be limited to the temperature range the internal sensor can report and I doubt the internal temperature can go that high. So the external sensor maybe OK to 185 F. You probably will not be able to read that high.

[fox7]

Here's a picture of the limitation I'm running into.

 

When programming the ISY, the pop-up values for temperature, only go up to 122.

 

Preventing me from testing a 140 to 150 range.

[LeeG]

Remember these are home thermostats. The 2441TH/2441ZTH have an operating spec of 39°to 104°F (4°to 40°C).

[Brian H]

The 2433A3 External Temperature Probe has a range of -13 to 185 degrees F.

I would not take that as an indication the 2441ZTH can also do the same range.

 

I am not a great Insteon Messaging person. So I maybe incorrect.

If I read the 2441ZTH's Developers Guide correctly and Smartlabs has not changed things. Your ISY choices are indicating

close to the maximum it can report. For both the internal and external temperature probes.

 

I am sure the folks at UDI will have further input for you.

[apostolakisl]

I guess ISY firmware needs an update to support the higher temps. Not sure why it doesn't already, perhaps there is a reason that isn't so simple. I am sure Michel will chime in with an answer to that.

 

A solution would be to use a CAI webcontrol board with a waterproof 1-wire temp sensor. The CAI can be programmed to post directly to ISY variables on any schedule or condition you like. Or, you could skip the ISY and program the cai board to cycle the recirc pump on its own.

[Brian H]

When you replace the internal sensor in the 2441ZTH with the external probe. As jmed999 did.

You are limited by what the 2441ZTH's hardware can do. It has a high limit in the mid 120 degrees F range.

So the choices in the ISY console. Are probably close to the top limit.

 

Since the external probe information is almost nonexistent in the 2441ZTH Developers Guide.

It is very possible that it can go higher on the external input and I was incorrect.

I believe there is no way at present to read the external probe data into the ISY controller.

 

The CAI webcontrol board sounds like a good way to go.

[LeeG]

The maximum temperature a 2441TH/2441ZTH could report (if it could) is 127.5 degrees.

 

The temperature is reported in a 1 byte field as temp * 0.5. The maximum value in 1 byte field is 255 (255 * 0.5 = 127.5). That is well past the published operating temperature range for 2441TH/2441ZTH of 39°to 104°F (4°to 40°C) and far short of the temperature ranges this topic is discussing.

 

The following is part of the Insteon traffic generated from a Query of a 2441TH. The temperature value returned is hex A6 decimal 166. 166 * 0.5 equals 83 degrees which is the current temp displayed on the thermostat. It is not physically possible for the Insteon message to contain the temperatures being discussed in this topic.

 

Sat 06/22/2013 09:28:39 AM : [iNST-TX-I1 ] 02 62 1D 6C D6 0F 6A 00

Sat 06/22/2013 09:28:39 AM : [iNST-ACK ] 02 62 1D.6C.D6 0F 6A 00 06 (00)

Sat 06/22/2013 09:28:40 AM : [iNST-SRX ] 02 50 1D.6C.D6 22.80.0B 2B 6A A6 (A6)

Sat 06/22/2013 09:28:40 AM : [std-Direct Ack] 1D.6C.D6-->ISY/PLM Group=0, Max Hops=3, Hops Left=2

Sat 06/22/2013 09:28:40 AM : [ 1D 6C D6 1] ST 166

[WhiteSax]

If one was willing to use a scale back number in the ISY programming, and if one was willing to calculate either a needed series resistor, or select a different resistance NTC thermistor - then it could be make it work. It would take some testing, but odds are the 2441ZTH internal sensor circuit is probably a voltage divider implementation of a 10K precision resistor in series with a 10K NTC thermistor. NTC thermistors decrease their resistance as temperature increases. The conversion model is likely based on the Beta Parameter equation (a simplification over the Steinhart–Hart equation).

 

Between the info here http://en.wikipedia.org/wiki/Thermistor and here http://learn.adafruit.com/thermistor you'll know enough to get the concept. If you have an electronics background - then it should be a bit easier.

 

You'd just have to accept that a reading of something like 95, might actually mean 145 due to the scaling (depending on what factor you calculate). Just remember that the ISY doesn't do floating point, and the 2441ZTH is only going to return 0.5degree increments.

 

In the end it's just math, some tinkering, and shopping research to find the right parts.

 

A fast way to just check the idea would be to put a 5K film resistor trim pot in series with the external sensor you have. Zero the trim, and place the sensor in a glass of warm water (say 100 degrees), then turn the trim pot to increase resistance, which will decrease the current running through the 10K sensing resistor, and make the temp look like a cooler temperature. Then you can try making the water in the cup hotter, and check if the temperature reading increases. This method will likely not give one for one linearity, but it should be proportional provided the water temp is in the operating range of the thermistor. If you are trying to control between two temps (say 140 and 150) then pick a resistance with the water at 145, and try to keep the 2441ZTH readings on the higher end. Next take readings at your two control points, and use those in your ISY programming.

 

Keep in mind that this is all based on the assumption that the 2441ZTH implemented a voltage divider sensor similar to the Beta equation method describe in the links above.

 

One last note: If the Beta being used by the 2441ZTH is about 4000, then it will take about 5.7K Ohms to get a 100F. Whereas a 2K thermistor reading would be about 150F. In this case a 3.7K series resistor would skew the 150F actual temp to read as 100F. The trick is knowing the Beta so one can calculate the expectant resistances needed.

 

Take some test measurements and do some calculations to determine what Beta is actually being used. Just put a 20K trim pot across the input, trim until the reading is 25 C. Then measure the resistance that provides the 25C reading. That is your Ro of the Beta equation (likely 10K). Then take some readings at higher pot values, representing temps colder than 77F (25C). Record the displayed temp, and record the resistance providing that temp. Do the same at lower pot values, representing temps hotter than 77F. Remember that the Beta equation uses Kelvin, so 1/To is not 1/25, but rather 1/(25+273.15). With the data collected solve for Beta. If the Beta values between high temp and low temp differ too much, then go with the Beta for the temp range that will be used in general for your situation.

 

Now you have enough data to either select a series resistor value, or select a new NTC Thermistor with a different Ro and similar Beta. Load the equations into a spreadsheet and play around with expected results to get comfortable with the model behavior. Then go shopping.

 

The graph below shows mapping of the skew, and why one should not expect a direct temp range skew of a fixed degree delta per change of temp. But for small temp ranges its a reasonable approach.

 

Good Luck

 

Enjoy.