Expedition Navigation Software 
1 - RagnarJW
- Expert
Offline - Registered: 5/15/2019
- Posts: 12
Using calibrated boat speed sent to GNX 120
Hello,
I have a B&G based system with GNX 120 mast displays. There is no central unit (Hydra, Hercules). I can calibrate the boat speed for the B&G instruments (Zeus3 plotter and H5000 graphic displays), they seem to share the calibration values and show the same calibrated values for boat speed. However, the GNX 120s show the uncalibrated value. The boat speed sensor is Airmax ST800 paddle wheel with NMEA2k output..
Having Expedition in the mix, I know Expedition can calibrate the boat speed input, but can it also send this calibrated value as custom value to the GNX displays? The manual says sentence "128259 Speed, water referenced" is available, but is this calibrated?
Thanks.
- Nick
- Moderator
Offline
- Registered: 9/16/2015
- Posts: 2,966
Re: Using calibrated boat speed sent to GNX 120
Yes, if you have told Exp to calibrate bsp. It would be nicer if you can get the calibrated bsp directly from the system though.
The DST has internal calibration tables, so it may be that these are being set but I don't know.
- RagnarJW
- Expert
Offline
- Registered: 5/15/2019
- Posts: 12
Re: Using calibrated boat speed sent to GNX 120
Thanks, Nick.
So just use BSP as the value in one of the custom fields? Or another value?
I have been looking for a way to directly calibrate the sensor, but there is no documentation on this. Most likely I would need a Hydra or Hercules to globally calibrate, but I am not sure if the data from the sensor would be replaced on the network.
- •
Thread Starter- Nick
- Moderator
Offline
- Registered: 9/16/2015
- Posts: 2,966
Re: Using calibrated boat speed sent to GNX 120
Yes.
There are a couple of displays that can calibrate them (maybe Maretron?). They can also be calibrated over NMEA 2000, but it is still on my work list.
- RagnarJW
- Expert
Offline
- Registered: 5/15/2019
- Posts: 12
Re: Using calibrated boat speed sent to GNX 120
The solution works. Many thanks, Expedition provided a good solution.
Maybe someone else reads this and can learn something, as I have.
With a system using so-called smart sensors transmitting their values directly into the NMEA 2000 network, you risk a classic garbage in, garbage out situation. The equipment vendors market these "easy installation" solutions, and they are easy to install. However, there is a price to pay: they do not give you easy control over the values the sensors transmit.
If you are concerned with having accurate data on your screens, use sensors connected to a server which calibrates and sends the calibrated value into the network. Perhaps in the future there will be editable calibration tables in the sensors themselves, which would solve the issue.
- •
Thread Starter- lutt
- Expert
Offline
- From: Oslo
- Registered: 4/05/2016
- Posts: 11
Re: Using calibrated boat speed sent to GNX 120
RagnarJW wrote:
With a system using so-called smart sensors transmitting their values directly into the NMEA 2000 network, you risk a classic garbage in, garbage out situation. The equipment vendors market these "easy installation" solutions, and they are easy to install. However, there is a price to pay: they do not give you easy control over the values the sensors transmit.
With my H5000 system this is not a problem (unless there's a caveat I do not know about). I can select the CPU as data source, which does all the calibration, instead of getting the unprocessed data from the sensor.
- RagnarJW
- Expert
Offline
- Registered: 5/15/2019
- Posts: 12
Re: Using calibrated boat speed sent to GNX 120
Do you have sensors transmitting on the NMEA2000 network, picked up by the CPU, calibrated, then re-sent as calibrated values? If so, how does that work, are there PGNs for uncalibrated and calibrated values, to differentiate between raw data and calibrated data?
- •
Thread Starter- lutt
- Expert
Offline
- From: Oslo
- Registered: 4/05/2016
- Posts: 11
Re: Using calibrated boat speed sent to GNX 120
I have not studied it in detail, so I can only guess; the b&g displays gets the preferred settings from the CPU, is the most likely in my mind. Again, just guessing so don't take it as fact.
I have seen on other systems with NMEA2k-bus that you can choose on each display what sensor to use for different things, so for interoperability between brands works fine if you have a h5k CPU and gnx displays.
(Secretly dreaming that my 20/20 mast displays breaks so I can defend the spend on replacing them with GNX120's)
- RagnarJW
- Expert
Offline
- Registered: 5/15/2019
- Posts: 12
Re: Using calibrated boat speed sent to GNX 120
I have not found a way to point the GNX displays to use a certain source for data. Agree that being able to filter out the raw data coming from the DST800 speed transducer would solve this particular issue. But it is a fudge, and as Nick says, much better to only have good, calibrated data on the network.
- •
Thread Starter- benhowett
- Expert
Offline
- Registered: 9/16/2015
- Posts: 32
Re: Using calibrated boat speed sent to GNX 120
I have not found a way to point the GNX displays to use a certain source for data.
Menu > Setup > Data sources.