Why are my Telegraph Transmitters not grounding correctly?

[ziadigi]

Hello,

My Telegraph Transmitters are in a 100mA loop that is supplied power through a Power Regulator. It appears that my connection to the ground point in the building is correct, but nothing codes out when it goes into ground mode, although I can hear the transmitter coding out correctly. What am I doing wrong?

This is part of a fire alarm reporting proprietary system. The grounds are being used as a backup method of connecting to the receiver

 

[berkeman]

Welcome to PF.

Hello,

My Telegraph Transmitters are in a 100mA loop that is supplied power through a Power Regulator. It appears that my connection to the ground point in the building is correct, but nothing codes out when it goes into ground mode, although I can hear the transmitter coding out correctly. What am I doing wrong?

This is part of a fire alarm reporting proprietary system. The grounds are being used as a backup method of connecting to the receiver

Holy smokes (sorry for the pun), you are working on a Fire Alarm reporting network, and having issues like this? Um, we can try to help you a little, but pretty quickly you will need to get somebody on-site that has more EE experience than you to help you sort this out.

What kind of "telegraph" communication network is this? Can you post a link to the physical layer specifications? And what communications protocol is it using? I'm familiar with 4-20mA signalling, but not 0-100mA signalling:

https://www.digikey.com/en/maker/bl...a-communication-protocol-and-how-does-it-work

And most communication networks are not grounded. They use floating twisted pair cable for noise rejection, and try to avoid ground faults (which introduce more noise into the TP network cable). An exception is RS-485 communication, which uses loosely grounded transceivers with extra common-mode range for the network connections (typically several volts outside the power supply voltages of the 485 transceivers).

 

[ziadigi]

Welcome to PF.


Holy smokes (sorry for the pun), you are working on a Fire Alarm reporting network, and having issues like this? Um, we can try to help you a little, but pretty quickly you will need to get somebody on-site that has more EE experience than you to help you sort this out.

What kind of "telegraph" communication network is this? Can you post a link to the physical layer specifications? And what communications protocol is it using? I'm familiar with 4-20mA signalling, but not 0-100mA signalling:

https://www.digikey.com/en/maker/bl...a-communication-protocol-and-how-does-it-work

And most communication networks are not grounded. They use floating twisted pair cable for noise rejection, and try to avoid ground faults (which introduce more noise into the TP network cable). An exception is RS-485 communication, which uses loosely grounded transceivers with extra common-mode range for the network connections (typically several volts outside the power supply voltages of the 485 transceivers).

Hi Berkeman,

Thanks for the quick response, I enjoyed the pun. I'm not messing with the system myself but I'm looking for documented resources that tell me how to correctly ground a system like this. Any resources or information is appreciated.

here is a link to the telegraph transmitter I'm working with.

https://www.digitize-inc.com/products/telegraph/425209-0001.php

Multiple people I know have said that the transmitter itself but when a technician pays them a visit it turns out that they just didn't connect it correctly.

 

[berkeman]

here is a link to the telegraph transmitter I'm working with.

https://www.digitize-inc.com/products/telegraph/425209-0001.php

Hmm, that has basic marketing info, but little in the way of installation instructions and a datasheet. So are these systems only installed by their technicians? And are you having problems with the communications right now and are trying to debug/fix it yourself? There does not seem to be enough information in that link to do any kind of debug, IMO.

Are you saying that you could call them to send a repair technician but would rather fix it yourself if you can? I'm not sure how the NFPA would feel about that...

 

[ziadigi]

Hmm, that has basic marketing info, but little in the way of installation instructions and a datasheet. So are these systems only installed by their technicians? And are you having problems with the communications right now and are trying to debug/fix it yourself? There does not seem to be enough information in that link to do any kind of debug, IMO.

Are you saying that you could call them to send a repair technician but would rather fix it yourself if you can? I'm not sure how the NFPA would feel about that...

No, I'm not saying that. I'm trying to gather what people are doing wrong as a whole because it has been the same problem (them grounding their transmitters incorrectly) so I can write informational content on what they're doing wrong when grounding their transmitters and how they can do it correctly.

This information is for fire alarm system distributors who receive documented information and live training on how to install these products.

I will try to find it and send it here, please give me a little bit.

 

[berkeman]

No, I'm not saying that. I'm trying to gather what people are doing wrong as a whole because it has been the same problem (them grounding their transmitters incorrectly) so I can write informational content on what they're doing wrong when grounding their transmitters and how they can do it correctly.

This information is for fire alarm system distributors who receive documented information and live training on how to install these products.

Have you talked with the company's Customer Support folks about your concerns? What is your experience in working with communication networks compared to their design engineers' experience?

 

[ziadigi]

Have you talked with the company's Customer Support folks about your concerns? What is your experience in working with communication networks compared to their design engineers' experience?

I'm a technical writer on the staff that takes recurring inbound questions going to tech support and writes (hopefully) educational content for people to refer back to in case there is a recurring problem across more than one client.

I just spoke with tech support downstairs. We don't have a "protocol" for the system according to the head guy, They're 3 or 4 ratio telegraph-coded transmitters.

 

[Tom.G]

The manual linked to in post #2,
(https://www.digikey.com/en/maker/bl...a-communication-protocol-and-how-does-it-work)

States:
"The Telegraph Loop Connection contains Integrated Lightning Protection via a printed circuit board mounted gas tube."

This indicates that a connection for a SAFETY GROUND is available and, along with the mention of Telegraph Loop Connection, indicate that the Telegraph circuit is a two-wire loop. This Telegraph Loop is floating with respect to Ground, see Ground Mode from the device Manual pg. 11, below.

From the OP's description, some users are tying one of the 100 mA Loop connections to Ground ...as a backup method..., which turns out to be counter-productive!

What am I doing wrong?

Tying one of the communication lines to Ground.

From the User Manual, pg 11:
Ground Mode

​

This is a backup method for transmitting an Alarm when an open loop condition exists. If a telegraph transmitter needs to make a transmission and detects an "Open Loop" condition, it will then switch to Ground Mode in an attempt to get the transmission through. At the same time, when an Open Loop condition occurs, the Form Four cards at the head end detect the open and apply a positive voltage to both sides of the loop and references earth ground as the negative side of the loop. The telegraph box sends the transmission coding the loop to earth ground.​

​

Cheers,
Tom

 

[Vanadium 50]

help you sort this out.

Before you sHort this out.