Exhaust temperature measure, boat

Updated 2022-06-10 !

In other posts I blogged about a way to measure temperature with a Raspberry Pi(RPi), direct connected or via WiFi, together with the marine applikation SignalK(SK). In this post I will follow up with a short brief about the practical solution, measuring exhaust temperature in a boat and sending an alarm if the temperature exceeds a set value .

In "wet exhaust" systems it is very important that the cooling water, injected in the exhaust system, always is present otherwise major damages can follow.

If you wan't to avoid a RPi check this post with approved NMEA 2000 temperature sensors from Yacht Devices 

Intro

The best way to monitor the exhaust temperature is to insert a temperature probe into the exhaust pipe about 150 mm after the water injection point. Other methods will be too slow avoiding damage.

Mechanical solution
As stated in the former post I used the temperature sensor DS18B20 to measure the temperature. In this case I will;

• Glue the probe, with epoxi, to a steel hose clamp
• Drill a 4 mm hole on top of the rubber exhaust hose
• Apply a small amount of marine sealant, Sikaflex 291, around the hole in the hose 
• Mount the assembly, probe pushed through the hole, onto the hose
• Tighten the clamp around the hose
• Connect the cable to the RPi

Software solution
In the former post I used Node-Red to measure the temperature and send it to SK. Here we must add a warning to the user of Wilhelm SK(WSK) if the temperature rises over a chosen temperature.

I will explain 2 ways;

• Via the plugin signalk-simple-notifications
• Via NodeRed 

Plugin
Install the plugin signalk-simple-notifications via the admin UI "Appstore => Available" and then configure with "Server => Plugin Config => Simple Notifications". 

• Mark "Active"
• Add "propulsion.port.exhaustTemperature" to the SignalK Path
• Add a text to the "Name" field
• Add the "High Value" where there should be sent an alarm. Note this value should be in Kelvin !!
• Set up the "Alarm State"
• And at the end click on "Submit"

Test it with WSK

Node - Red
To fix this I added some code to my former application and used the 2 SK Nodes send alarm and clear alarm. 

To pick the exhaust temperatures I use signalk-subscribe nodes.

Since the exhaust temperatures are created with Node-Red it is very important You set the $Source property in the signalk-subscribe node to signalk-node-red.

In the switch node, test is made against the threshold values and sent on to the appropriate alarm function. The notification path is set to either ptExhaustTemp or sbExhaustTemp 

You can easily check the status, in a web browser, with the url

http://yourhost:3000/signalk/
v1/api/vessels/self/notifications

and in WSK

Node-Red code