DLT clock gains time

Hi,

I've had my CBUS system for almost three years and it runs perfectly ever since setup. There is only one niggle and that is that the clock on my DLT units gains a few minutes every couple of months.

There is no clock signal other than when I change the time on a DLT - whilst there is a PAC in the system, it is plugged into a laptop running Harmony all the time so I don't think it can issue any of its own commands whilst it is letting Harmony do its work (which doesn't seem to feature a clock setting option).

Is there anything I can do about this, and why it happens? All the clocks on all the DLTs seem to run fast, so they're either all running on the same slightly fast clock hardware or the clock signal perhaps gets sent from one erroneous device? How often does the clock signal go through the system when there is nothing other than the DLTs keeping the time?

Thanks for any help.

Pat

 

If the PAC has another system connected to it's USB port permanently, then it's just functioning as a USB PCI. It won't participate in any time keeping. Incidentally, why use a PAC and not a USB PCI for this purpose?

The issue of time drift is because you have no devices on your network that can function as a real time clock.

Note: The C-Bus Communication clock and the time keeping clock messages are not the same thing.

The only time DLT's broadcast the time on the network is when the time is set from a DLT. Other than that special case, they only listen for time broadcasts by other devices.

The reason for the drift is because the time in the DLT is synchronised to the C-Bus communication clock pulses. The network clock pulses are timed from a 30-50ppm crystal, which works out to be a theoretical worst case of about 26 minutes per year.

The PAC does have a real time clock, and will function as a master time keeping device on the network, so the best solution is to move the harmony system over to a USB PCI and then let the PAC do it's stuff. You will need to download a project to the PAC via PICED which will make sure your PAC has the latest firmware and also has any Daylight Saving schedules included.

Another option is to change the unit that is currently acting as your C-Bus Clock generator. One of your output or systems units on the network will be generating the C-Bus communication clock and it might just be on the upper end of the frequency tolerance for the crystal. You can see which unit is currently generating the network communication clock by looking on the Status tab of your Output and System units UI's in Toolkit.

To do this, enable the ability to be the C-Bus clock generator on another unit first. This is to prevent you getting into the situation where your C-Bus network has no C-Bus communication clock generators on the network and without one your network can't communicate. It's usually on the Global tab for a unit in Toolkit. Then, go to the unit that is currently generating the network clock and disable the Clock generator function on that unit. This will transfer the responsibility for generating the C-Bus communication clock from the current unit to another unit on the network.

 

Brilliant answer thank you.

I have a serial PCI I could use (USB ones didn't exist when I got the system I believe) - they're in different parts of the house however - I have a set of dimmers/relays in the cellar and same again in the loft and I wanted to be able to remotely administer the system because the PAC is in the loft... meaning it's handy it's always plugged in, so all I have to do is control the laptop to shut down harmony and fire up the toolkit if needed.

I do see what you're saying though. I'll look at moving the PCI upstairs and let the PAC do its job - I presume I can't program the PAC via the PCI though, it'd need to be plugged directly in?

Pat

 

You can program a PAC over C-Bus but it's so slow and tedious that it's really not worth the bother.

If your USB is always plugged into the PAC then you've obviously not using any of the PAC functions. If you free it up, I'm sure you'll discover lots of useful things to do with it.

If remote admin of the system matters to you, have you considered a Wiser, or at least a C-Bus Ethernet interface? That way all you need to do is be connected to your ethernet infrastructure to access your system. I find it quite convenient to reprogram the system from the convenience of a laptop whilst sitting on the sofa, using WiFi to connect to the Wiser on my LAN.