Published by pchipkin March 28th, 2008
in BACnet MSTP and RS485.
Lets say you adopted all the best practices for installation of the network but you get intermittent or unacceptable performance because of packet loss, noise, collisions … Then you should consider hiring an expert to resolve your problems because now you are in the ‘Art’ part of RS485. These are some of the things they […]
Did you like this post?
Subscribe To The RSS Feed!
To catch many more articles like this in the future, make it easy on yourself and subscribe to me via RSS. You will not regret it!
Do you have a question?
We will do our best to try and solve any building automation, protocol, integration problem you may have
Published by pchipkin March 27th, 2008
in BACnet MSTP, Cables and RS485.
All cables offer impedance (resistance). Some cables are designed so that the impedance is relatively independent of distance. You want one of these cables. A clue to knowing if you selected one is to look at the cable’s Nominal Impedance. If they quote a number such a 100Ohms you have a good cable. If they […]
Did you like this post?
Subscribe To The RSS Feed!
To catch many more articles like this in the future, make it easy on yourself and subscribe to me via RSS. You will not regret it!
Do you have a question?
We will do our best to try and solve any building automation, protocol, integration problem you may have
Published by pchipkin March 19th, 2008
in BACnet MSTP and Cables.
Practically speaking you can go up to 4000 feet (1200m) at baud rates up to 76800 baud. Above that you need to do a little math and reduce the length. For example, at 115k baud your cable should not be much longer than 2500 feet.
However, the higher the baud rate the more sensitive the cable is […]
Did you like this post?
Subscribe To The RSS Feed!
To catch many more articles like this in the future, make it easy on yourself and subscribe to me via RSS. You will not regret it!
Do you have a question?
We will do our best to try and solve any building automation, protocol, integration problem you may have
Published by pchipkin March 18th, 2008
in BACnet and BACnet MSTP.
Data inside a BACnet device is organized as a series of objects. Each object has a type and a set of properties. There is always at least one object in a device – it is used to represent the device itself . The other objects represent the device’s data.
In practical terms think of a simple […]
Did you like this post?
Subscribe To The RSS Feed!
To catch many more articles like this in the future, make it easy on yourself and subscribe to me via RSS. You will not regret it!
Do you have a question?
We will do our best to try and solve any building automation, protocol, integration problem you may have
Published by pchipkin March 17th, 2008
in BACnet and BACnet MSTP.
All devices on a BACNet network are effectively peers. This means that any device (we take device here to mean any Bacnet capable entity – device or software application) can write to the writable properties of another device’s objects. This can result in conflicting commands.
BACnet has a mechanism to resolve the conflict. It differentiates between […]
Did you like this post?
Subscribe To The RSS Feed!
To catch many more articles like this in the future, make it easy on yourself and subscribe to me via RSS. You will not regret it!
Do you have a question?
We will do our best to try and solve any building automation, protocol, integration problem you may have
Published by pchipkin March 14th, 2008
in BACnet MSTP and RS485.
How many devices to install on a single RS485 Trunk (Bandwidth Issues). There are non electrical considerations to determine how many devices you put on an MSTP network.
The chart below illustrates (from one installation) how little of the bandwidth is used to transfer data. The APDU’s are application layer message that poll and respond with […]
Did you like this post?
Subscribe To The RSS Feed!
To catch many more articles like this in the future, make it easy on yourself and subscribe to me via RSS. You will not regret it!
Do you have a question?
We will do our best to try and solve any building automation, protocol, integration problem you may have
Published by pchipkin February 26th, 2008
in BACnet MSTP.
(To provide clarity this article does simplify the issues to some extent.)
BACnet MSTP is a token passing protocol. Only nodes with the token are allowed to initiate service requests such as requests for data. A device that receives a request, a request that requires a response, may respond without having the token.
Based on this behavior […]
Did you like this post?
Subscribe To The RSS Feed!
To catch many more articles like this in the future, make it easy on yourself and subscribe to me via RSS. You will not regret it!
Do you have a question?
We will do our best to try and solve any building automation, protocol, integration problem you may have
Published by pchipkin December 14th, 2007
in BACnet MSTP.
A BACnet MSTP device should search for a new master after it has gotten the token more then Npoll – 1 times.
If your device is on a large network (20+ nodes) and Npoll is set to a very high number it may take a long time for your device to find a new device […]
Did you like this post?
Subscribe To The RSS Feed!
To catch many more articles like this in the future, make it easy on yourself and subscribe to me via RSS. You will not regret it!
Do you have a question?
We will do our best to try and solve any building automation, protocol, integration problem you may have
Published by pchipkin December 14th, 2007
in BACnet MSTP.
Tusage_timeout
The minimum time without a DataAvailable or ReceiveError event that a node must wait for a remote node to begin using a token or replying to a Poll For Master frame: 20 milliseconds. (Implementations may use larger values for this timeout, not to exceed 100 milliseconds.)
Nretry_token
The number of retries on sending Token: 1.
Tusage_timeout variable is […]
Did you like this post?
Subscribe To The RSS Feed!
To catch many more articles like this in the future, make it easy on yourself and subscribe to me via RSS. You will not regret it!
Do you have a question?
We will do our best to try and solve any building automation, protocol, integration problem you may have
Multi-state objects are very important in operational state description of a BACnet device. There are three types of Multi-state objects described in the BACnet standard:
Multi-state Input
Multi-state Output
Multi-state Value
All three object types use the four required BACnet standard properties. Refer to the article on BACnet Objects by the same author for a more detailed explanation.
The Multi-state […]
Did you like this post?
Subscribe To The RSS Feed!
To catch many more articles like this in the future, make it easy on yourself and subscribe to me via RSS. You will not regret it!
Do you have a question?
We will do our best to try and solve any building automation, protocol, integration problem you may have