Temporary Monitoring Application

Good afternoon,

I am currently investigating using an emonTx4/emonVs/emonBase system as a temporary monitoring device to measure site level grid import and export over a weekly period.

The OpenEnergyMonitor guide has been useful for learning about your devices and I believe the system is suitable for my application. As I am completely new to electronics, it would be helpful to get some further clarification and guidance before I purchase any components and get started:

  1. Can an emonTx4/emonVs/emonBase system measure power import and export? Other systems I have investigated and tested have been unable to measure grid export and cannot measure the direction of power flows. Is the emonVs voltage measurement necessary for this (I can’t find this referenced in the docs!)?

  2. As the system would be used as a temporary monitoring device and would be installed/removed regularly, it would be preferable to use flexible coils (see https://www.echun-elc.com/productsShow.asp?id=445) because they are easier to install than the clip-on alternatives. Are the flexible coils compatible with the system?

  3. Can the emonBase store data locally onto an SD card? This is important for the intended application as there is often no wifi access where the systems are installed.

Any help with the above would be much appreciated.

Many thanks!

Welcome, Adam, to the OEM forum.

Some answers for you:

  1. Yes to both. Without the voltage reference, it’s impossible to determine the direction of power/energy flow. As a rider to this, there’s a ‘Learn’ section here with some basic (and some quite advanced) theory about energy monitoring. I don’t suggest you try to learn it all, but it’s well worth knowing it’s there. There’s a link at the top of every page of the forum site.

  2. I don’t think anyone has ever used a Rogowski coil with any OEM device. We don’t do the conditioning amplifier you need to turn the output into a usable voltage, so everything would depend on the output of this and hence its compatibility with our c.t. input (0.333 V rms, referenced to ground for the emonTx4). There’s a wide range of compatible c.t’s available over and above those available from our shop.

  3. “emonBase” is a generic term - it can cover the one sold in the OEM shop, it can also refer to a server of your own. The OEM-Shop emonBase is a Raspberry Pi with a radio receiver to accept data via ISM-band UHF radio from the emonTx4, so inherently all data and the operating system and application program (emonCMS) are on the (only) SD card. You need Wi-Fi or wired Ethernet, a router and a computer with a web browser to set up the data recording, and to view the data, thereafter you don’t. You could take your LAN (Ethernet or WiFi) with you to download the data; or it’s conceivable that it would be possible to take a spare SD card with exactly the same configuration and swap cards - with some data loss because of course the system must be shut down before the SD card is removed.

Feel free to ask as many questions as you feel you need.

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Hello @EdamCheese and thanks Robert, a small additional note for use without active internet connection is that the emonBase does rely on an internet connection in order to synchronise the local system time. If you set it up initially with an internet connection to get the time and do all of the other configuration that can work but it will lose the time if it is power cycled after disconnecting the internet. It’s possible to use a RaspberryPi RTC to get around this, there are a number of guides available on how to do this, but it’s not something we have tried/tested recently so cant be 100% which one is best. Here’s one from a quick google search Adding a Real Time Clock (RTC) to the Raspberry Pi - Pi My Life Up

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We stock RTCs in our online store, we can pre-fit one to an emonBase before shipping if ordered together:

Thanks for all your help, it’s much appreciated.

I will get back in touch if I have any further questions.