The two most common forms of BACnet communications channels that you are likely to encounter are BACnet MS/TP over RS-485 and BACnet/IP over Ethernet. Every device on a channel must use the same type of communications. To transmit data between channels of different types you must use a router.
1.) BACnet MS/TP - This channel is a 9.6 kbps - 76.8 Kps twisted pair channel. I/A Series BACnet controllers are delivered with MS/TP transceivers. I/A Series BACnet controllers (MNB-300, MNB-1000, MNB-V1, MNB-V2, etc.) must be on an MS/TP channel. MS/TP channels must be configured as a POLARITY sensitive RS-485 BUS topology.
The RS-485 BUS should use LOW IMPEDANCE 22 AWG or 24 AWG twisted shielded cable with a distributed capacitance between conductors of less than 15 pF/ft and a characteristic impedance between 100-130 Ohms. Belden 89841 is commonly recommended and can be used with confidence. I recommend that a maximum cable length of 2500' be observed.
2.) BACnet/IP - This is a TCP/IP channel. This channel is typically an Ethernet backbone from which other BACnet MS/TP channels are derived to create a network. Maximum cable lengths are subject to standard Ethernet wiring rules. 10/100 BaseT segments cannot exceed 328 feet.
Here is what I have been recommending:
Windy City Wire:
1-800-379-1191
BACnet MS/TP 24 AWG:
http://harrier.smartwire.com/ecom/invmainprof.php?item=042002-S
BACnet MS/TP 22 AWG (increased physical strength and works with ARCnet):
http://harrier.smartwire.com/ecom/invmainprof.php?item=043006AL-S
Belden 89841 is commonly recommended by manufacturers of BACnet equipment and can be used with confidence.
If you know of a better method, please let me know!
Wednesday, June 6, 2012
Thursday, May 31, 2012
Monday, May 14, 2012
Converting a Binary Output to an Analog Output Using PWM (Pulse Width Modulation)
I recently ran into a situation where I needed an additional analog output on a Schneider Electric IA Series BACnet (MNB300) Controller.
I was able to accomplish this by providing a pulse width modulated output from one of the triac outputs. Essential, a pulse width output communicates an analog number between 0 and 100% by keeping the binary output on for a percentage of some given time base. For example, if your time base is 10 seconds and your binary output is on for 5 seconds, then you would be communicating that you wanted to analog output at 50%.
In this case, I wanted a 2 - 10 volt signal for an actuator. I used a PWA-1A from Kele.com to convert the pulse width modulated binary output from my MNB300 into a 4-20ma signal. Then I simply installed a 500 ohm resistor accross the output to make convert the 4-20ma signal into a 2-10 volt signal.
Schneider's Workplace Tech software makes configuring a binary output as a pulse width modulated output easy by providing a PWM software block that can be used to configure the binary output.
Here is my wiring diagram.
I was able to accomplish this by providing a pulse width modulated output from one of the triac outputs. Essential, a pulse width output communicates an analog number between 0 and 100% by keeping the binary output on for a percentage of some given time base. For example, if your time base is 10 seconds and your binary output is on for 5 seconds, then you would be communicating that you wanted to analog output at 50%.
In this case, I wanted a 2 - 10 volt signal for an actuator. I used a PWA-1A from Kele.com to convert the pulse width modulated binary output from my MNB300 into a 4-20ma signal. Then I simply installed a 500 ohm resistor accross the output to make convert the 4-20ma signal into a 2-10 volt signal.
Schneider's Workplace Tech software makes configuring a binary output as a pulse width modulated output easy by providing a PWM software block that can be used to configure the binary output.
Here is my wiring diagram.
If you know of a better method, please let me know!
Thursday, October 6, 2011
Energy Management: You Can't Manage What You Don't Measure
This little meter was easy to configure and easy to use. This device makes monitoring consumption in real time easy. For $129, that's impressive.
That is certainly the case with Energy Management. Information allows you to make informed decisions and can often uncover things that are unexpected.
Last week I installed a Current Cost ENViR energy meter in my home. This is a "whole house" meter that connects to the main electrical supply entering entering my home. It has two clamp on current transmitters and a programmable voltage (it does not require voltage taps). It also has a wireless transmitter to transmit the consumption data from the electrical panel to a nice little display.
I have put the display unit in my kitchen where we can see what the current consumption is at any time of the day. As time goes on, we are getting a feel for what our "baseline" is. When we are above the baseline, the obvious question is "what is running that should not be?".
This weekend, we plan to shut everything off and then turn on one device at a time and figure out how much energy it draws. We will enter each device and its draw into a spreadsheet and figure out which are the worst culprits and what actions we can take to minimize their use or if we should replace them.
I have already noticed that the dryer is a big drag on my wallet. I notice that we are usually using about 600 watts in the morning, but we were almost 3 times that the other day when the dryer was running. Air drying is beginning to look like a good idea!
Monday, October 4, 2010
Green Energy - A Watt saved is a Watt earned.
This blog post might get me into trouble.
This is a case where I think my opinion is shared by many in our industry who are just afraid to speak up for fear of losing business or being ridiculed.
Money spent on most green energy technologies is wasted!
There I said it. Every dollar that is spent to GENERATE green energy, could be better used to SAVE energy.
Perceptions are the Problem:
Energy conservation methods do not have the sex appeal that new forms of generation do. The reality is that we already have ways to generate lots of energy cheaply without foreign oil or creating greenhouse gases. Nuclear Energy has served us well. If one were to calculate the cost in human lives for each Watt of energy consumed in the United States by Nuclear Generation and any other major source, you would find that Nuclear Energy is the cleaner, safer, alternative.
I am sure that our electrical founding father, Benjamin Franklin, would agree that a Watt saved is a Watt earned.
I admit that energy conservation efforts are not sexy, but they are a better investment than green generation (assuming that we do not consider subsidies). There is a lot of room in my industry for improvement, but it is a difficult sell. The savings lie in software and improved methods to reduce consumption that will have little or no visible impact and may result in reducing human comfort (gasp).
As an example, ENE Systems has developed a clever Optimal Start / Optimal Stop OPC Server that can connect to most commercial control systems to start temperature control equipment at the last possible minute to achieve set point prior to occupancy. Without this type of software, achieving set point prior to occupancy is normally done by turning on the equipment on an hour or more prior to occupancy to make sure that the space has a chance to warm up.
I have a lot more to say about this subject, but this is enough for today's post. Stay tuned for: "You get what you measure".
This is a case where I think my opinion is shared by many in our industry who are just afraid to speak up for fear of losing business or being ridiculed.
Money spent on most green energy technologies is wasted!
There I said it. Every dollar that is spent to GENERATE green energy, could be better used to SAVE energy.
Perceptions are the Problem:
Energy conservation methods do not have the sex appeal that new forms of generation do. The reality is that we already have ways to generate lots of energy cheaply without foreign oil or creating greenhouse gases. Nuclear Energy has served us well. If one were to calculate the cost in human lives for each Watt of energy consumed in the United States by Nuclear Generation and any other major source, you would find that Nuclear Energy is the cleaner, safer, alternative.
I am sure that our electrical founding father, Benjamin Franklin, would agree that a Watt saved is a Watt earned.
I admit that energy conservation efforts are not sexy, but they are a better investment than green generation (assuming that we do not consider subsidies). There is a lot of room in my industry for improvement, but it is a difficult sell. The savings lie in software and improved methods to reduce consumption that will have little or no visible impact and may result in reducing human comfort (gasp).
As an example, ENE Systems has developed a clever Optimal Start / Optimal Stop OPC Server that can connect to most commercial control systems to start temperature control equipment at the last possible minute to achieve set point prior to occupancy. Without this type of software, achieving set point prior to occupancy is normally done by turning on the equipment on an hour or more prior to occupancy to make sure that the space has a chance to warm up.
I have a lot more to say about this subject, but this is enough for today's post. Stay tuned for: "You get what you measure".
Tuesday, June 16, 2009
BACnet over the Internet
In general, BACnet is a broadcast network protocol. For this reason it is not well suited to use over a wide area network, or the Internet. To facilitate the transport of BACnet information over a WAN the BBMD (BACnet Broadcast Management Device) was introduced.
I like to compare the operation of BBMDs with the operation of a CB radio. On the local network all controllers can "hear" each other talking as would everyone in the cab of a truck when one person talks into their CB. The communications are then sent to other BBMDs over the wide area network that are aware of each other (each BBMD must be aware of every other BBMD, like being on the same CB channel). On the receiving end, all controllers "hear" the remote device's broadcast on their local network as would everyone sitting in the cab of a truck receiving a CB transmission.
That said, the use of BBMDs makes BACnet over a wide area network possible. At each site a BBMD is needed. Each BBMD must be programmed to know about every other BBMD that will be part of the system. The front end must have either a local BBMD or act as a foreign device to at least one of the remote BBMDs.
Monday, April 13, 2009
Lonworks Over Fiber
Recently I had a situation where I had to run lonworks over fiber (the lonworks wiring was too close to power wiring). At one time in the past, I had tried fiber by lon routers and although it worked, my experience was not very good.
For this job I am going to try:
(2) Black Box Corp. LBH100A-H-ST
(2) Echelon i.LON600 (24 VAC)
(2) Cabinets as appropriate for conditions on either side of the fiber run.
(2) 50 VA Transformer for i.LON600
Copper from the near iLON600 or a switch where i.LON600s are connected will go to the first media converter. Then fiber will traverse the distance in question. On the far side, the fiber will enter the 2nd media converter and exit as a 2nd copper segment. This second copper segment will enter the iLON600.
For this job I am going to try:
(2) Black Box Corp. LBH100A-H-ST
(2) Echelon i.LON600 (24 VAC)
(2) Cabinets as appropriate for conditions on either side of the fiber run.
(2) 50 VA Transformer for i.LON600
Copper from the near iLON600 or a switch where i.LON600s are connected will go to the first media converter. Then fiber will traverse the distance in question. On the far side, the fiber will enter the 2nd media converter and exit as a 2nd copper segment. This second copper segment will enter the iLON600.
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