FF signal , DD file & VCR

[RAJESHVM]

Hello everybody ,

This is my first bunch of quaries, hope will get answers,

AA) I understand, power supply is a DC voltage and comm. signal an AC voltage, which is changing the current flow on fieldbus cable -

Q-1)In this case current will toggle in 32 micro second ? The toggling of current is also depends on series of '0' and '1' ?
Q-2) who is togglling the current on fieldbus cable ?
Q-3) What will be the value of votage signal (p-p) ?

BB) What is VCR ? How communication is done through VCR ?

CC) I understand DD file is a driver for FF devices & is a text file,
Q-1) HOw text file can be used as a driver for a device ?
Q-2) What is roll of .cff,.sym,.ffo during communication ?

Thanks !
Have nice week end.

[rezabejd]

Q-1)In this case current will toggle in 32 micro second ? The toggling of current is also depends on series of '0' and '1' ?

It works as advertised. 35 KHz or thereabouts. As an end-user, my main concern is that it works reliably. It does. Sometimes we use a scope meter to look at the waveform; then this nuance of the technology is handy to know.

Q-2) who is toggling the current on fieldbus cable ?

Each device on a segment originates a signal. Some messages are "published" and others are "polled" using token passing. The "Link Master" coordinates the clocks of all devices and performs the token-passing.

Q-3) What will be the value of voltage signal (p-p) ?
I think 150 mV P-P is the minimum. Typically it's closer to the range 500 mV to 800 mV, at least in our plant.

BB) What is VCR ? How communication is done through VCR ?
VCR stands for "virtual communications (?) relationship" in fieldbus-speak - I think. If you have a significant number of multi-variable devices - for example, a dozen Rosemount 848T's each supporting 8 AI's, all on a single statement, you might have to care about VCR's. Some host H1 interface cards (where the link master / Link Active Scheduler = LAS lives) have a lower limit (total VCR's) than others. I have many segments with over 14 devices and have only hit the limit once (on my vendor's card).

CC) I understand DD file is a driver for FF devices & is a text file,
Q-1) HOw text file can be used as a driver for a device ?

Remember ".ini" files from Windows 9x days of yore? I still see them in XP but I never look at them any more - a good thing. They were text files that told the OS how to use certain devices. The DD is a "standard" way of telling diverse host systems what all a given device has to offer. The main concern of end-users is that they work with their host, and work as well as they do on the "same vendor" host (e.g. Rosemount 3051 on DeltaV) as they do on "unlike vendor" host (e.g. Fisher DVC6000 on CS-3000). There have been some complaints but the new DD standards release will go further than before to make sure everyone plays well together.

Talk to your host vendor and make sure they have plans to fully support the latest DD standard.

Q-2) What is roll of .cff,.sym,.ffo during communication ?
Not sure. I see them when I unzip a DD, but I just point the host to the directory where they are unzipped and the rest of the process is transparent.

HTH
John Rezabek
ISP

[sgadre]

Hi Rajesh,

Answers to most of the questions have been answered in the first reply. Here is some additional information.

What will be the value of voltage signal (p-p) ?
The p-p value of the signal voltage shall be between 700 mV to 900 mV in a ‘Normal’ network with 2 terminators connected.
If one of the terminators is missing (disconnected, loose contact), the p-p voltage amplitude will increase and will be more than 1.5 V. This characteristic is in fact used for troubleshooting the Fieldbus Network.
If an additional terminator is connected then the signal amplitude will get more attenuation and it will be nearly 500 to 600 mV. Again this is used for troubleshooting and removing the additional & un-necessary terminator from the network

The value of the amplitude also depends upon where you measure it and the reliable measurement will be at Trunk Side. The values above are for the trunk side measurement. At spur side after the Field Connectors which provide the spur short-circuit protection, the values may be little different.

Regards,

Sagar

[Mike Stathopoulos]

Great answers! For a more thorough understanding (and bed-time reading) of the entire technology-scope fundamentals, read our Technical Overview guide from our website. It's a primer for device & host developers. BTW: signal is 0.75-1.0 V p-p (fig. 39 in tech. ovw.)

Technical Overview (http://www.fieldbus.org/images/stories/technology/developmentresources/development_resources/documents/techoverview.pdf)

Cheers,
Mike

[marisg]

You might get some of your questions answered in Relcom's Fieldbus Wiring Guide, www.relcominc.com (http://www.relcominc.com)

[tboyd]

You will find answers to most if not all of your questions in our FOUNDATION fieldbus Primer which can be found on our website at the following URL: http://www.fieldbusinc.com/downloads/primer1_1.pdf

[RAJESHVM]

Great answers! For a more thorough understanding (and bed-time reading) of the entire technology-scope fundamentals, read our Technical Overview guide from our website. It's a primer for device & host developers. BTW: signal is 0.75-1.0 V p-p (fig. 39 in tech. ovw.)

Technical Overview (http://www.fieldbus.org/images/stories/technology/developmentresources/development_resources/documents/techoverview.pdf)

Cheers,
Mike

Thanks.

Good Morning Mr.Mike/ Mr. Sagar,

I do agree with you as a theoretical point of view or may be in case of one FF device.
If i have connected 10 devicess, then total base current will be 10x10 = 100 mA, and the current will toggle between 91 to 110 mA, in this case what will be the voltage singal (p-p) ?
If it is still 0.75-1.0 V(p-p) how it will be possible as base current it self is 100mA ?
I may be missing something pls. clarify it.

Rajesh.

[RAJESHVM]

Hi Rajesh,

Answers to most of the questions have been answered in the first reply. Here is some additional information.
What will be the value of voltage signal (p-p) ?
The p-p value of the signal voltage shall be between 700 mV to 900 mV in a ‘Normal’ network with 2 terminators connected.
If one of the terminators is missing (disconnected, loose contact), the p-p voltage amplitude will increase and will be more than 1.5 V. This characteristic is in fact used for troubleshooting the Fieldbus Network.
If an additional terminator is connected then the signal amplitude will get more attenuation and it will be nearly 500 to 600 mV. Again this is used for troubleshooting and removing the additional & un-necessary terminator from the network

The value of the amplitude also depends upon where you measure it and the reliable measurement will be at Trunk Side. The values above are for the trunk side measurement. At spur side after the Field Connectors which provide the spur short-circuit protection, the values may be little different.

Regards,

Sagar

Quate :-
Thank you Mr. Sagar.

Can you pls focus more on Q-2 of quaries ?
I am not clear about the roll of DD file during communication on FF cable.
I think, as DD file is kept in Host system, there is no roll during the communication between device to H1 card. It will come in function during communication between H1 card and host system.



Thanks.
Rajesh

[Mike ONeill]

Rajesh,
If the devices all take 10mA each then the base DC current is, as you say, around 100mA. The one device that is transmitting at any one time 'toggles' its current +/- 10mA, so the actual measured current is 90 to 110mA - all other devices stay steady.

The +/-10mA goes into & out of the termination resistance (2x 100 Ohms in parallel equals 50 Ohms) and so the ideal signal voltage measured is around 1V pk/pk (20mA pk/pk into 50 Ohms = 1V pk/pk).

In reality, the segment cable will have some resistance which is also in series with each terminator and effectively unbalanced (since the transmitter is normally well towards one end of the cable), making is some additional attenuation along the length of the cable and the measured voltage deviate from the ideal 1V pk/pk depending on exactly where you measure it.

[Heather Santos]

Q-2) What is roll of .cff,.sym,.ffo during communication ?

CFF (Capability File) is used to configure a device offline. If your host system supports offline configuration, this file is used to create a template of the device. Configuration beyond the initial appearance of the device will not affect the contents of the CFF.

FFO, SYM (Device Description files) are used during on-line communication with the device. The DD files decode the packets for the person reading the HMI/GUI. It provides the label, help text, decimal place, units, menus and methods. The new version of these (FF5, SY5) files support visualization such as graphs, charts, images, also persisted data.

[RAJESHVM]

Q-2) What is roll of .cff,.sym,.ffo during communication ?

CFF (Capability File) is used to configure a device offline. If your host system supports offline configuration, this file is used to create a template of the device. Configuration beyond the initial appearance of the device will not affect the contents of the CFF.

FFO, SYM (Device Description files) are used during on-line communication with the device. The DD files decode the packets for the person reading the HMI/GUI. It provides the label, help text, decimal place, units, menus and methods. The new version of these (FF5, SY5) files support visualization such as graphs, charts, images, also persisted data.



Thank you Sir,

DD file is not a executeble file then in this case how it will decode the data received from FF device (data packets of which is series of preamble,start de., End del. & Data) ?

Which are the different methods provided by DD file ? What is it's purpose ?

Rajesh.