Tuesday 31 January 2012

Power Over Ethernet


Jargon

Powered Devices (PD)

The device being powered.

Power Sourcing Equipment (PSE)

The device supplying the power

Endspan PSE

Also known as POE Switches. The switch (or other network endpoint) supplies the power.

Midspan PSE

The Power is injected onto the cable outside of the network end point. You use Midspan PSE’s when you are using a standard switch with no POE capability but you want the Ethernet cable to carry the power to the field device. You thus inject power at a ‘midpoint’

Modes

This jargon term is used to define whether power is carries on the data lines or the spare line. The PSE determines the mode. The standard requires that PD’s support both modes. The PSE may not activate both modes at the same time.

Mode A

The data lines also carry the power.

Mode B

Spare or non-data lines carry the power.

POE Power Class

A term that describes the amount of power supplied. The PSE sets the class based on how the PD signals it for power. During the start up phase, the PD draws a specific amount of current. This tells the PSE what class to operate at.

Class Power In Watts Classification Current mA
0 0.44 to 12.95 <5
1 0.44 to 3.84 10.5
2 3.84 to 6.49 18.5
3 6.49 to 12.95 28
4 Reserved 40


POE Powering Stages

A PSE must never send power to a device that does not expect it. For this reason power is not simply applied when a connection is made. Rather the PSE progresses through these powering stages.



Signature

PSE probes the device to see if it is 802.3af compliant by looking for a signature impedance of 25kOhm using a voltage of between 2.7 and 10V. If the signature is not seen then the process terminates and no power is supplied. The Signature stage restarts when cable is reconnected.



Classification

PSE supplies a voltage and the PD draws a specific current. Based on the current draw the PSE determines the power class to be supplied.



Startup

The PD starts up as the supplied voltage reaches a level sufficient for the device to operate normally.



Normal Operation or Disconnect

If you remove the cable the PSE stops supplying power. Reconnection means that the powering stages begin again with the signature stage. If the PD stops using the supplied power (draws less than 10mA for 400mSec) the PSE stops applying power returns to the signature stage.



Watch Out for



Two Issues – hotter cables and hotter switches

Some of the power supplied will be lost as heat in the CAT5 cable. Heat degrades the insulation (at best) or causes fires at worst. Based on the 802.3af spec the TIA permits a max of 100 CAT5 POE cables to be bundled together. Thus is based on the spec of 350mA. There are devices that can supply more current and hence the heat issue becomes more pronounced.

The POE switches will draws more power and hence dissipate more heat from internal losses.



Polarity

The POE standard does not specify which lines will carry the positive voltage and which will carry the negative voltage. If the PD meets the POE spec there are no issues. If it doesn’t then you could end up with a polarity reversal and damage.




Some device use non-data lines in the CAT5 cable for other purposes such as voice. If such a device was connected to a PSE that doesn’t meet the POE standard then it could be supplied a voltage it doesn’t expect and this could cause damage.



Connecting non POE devices

Not an issue of the PSE meets the standard because it won’t apply power unless the field device presents the correct signature. If it doesn’t meet the spec, power could be applied continuously which means the the non POE field device could see a voltage that it wasn’t designed for and this could cause damage.



Voltage Level

Different vendors have implemented POE at different voltage levels. These PSE’s are non standard.

Eg.

Cisco 48V

Intel 12V or 24V

Symbol 12V or 24V

Apple 48V


Monday 30 January 2012

Trouble Shooting BACnet MSTP

One badly behaved device on a MSTP trunk can cause a collapse in performance.

To understand why consider this one example of what can go wrong. RS485 is s shared trunk. When two devices transmit at the same time this causes a collision. In simple terms think of the messages interfering with each other and corrupting each other so neither message is recognizable. To prevent this happening and to allow for multiple master on a network, BACnet has chosen a token based system. Only devices with the token can initiate a message transaction. To keep things running smoothly, BACnet has some demanding timing requirements. For example, a device passes the token on. The receiving device has 15msec to use the token. Lets say it responds in 18msec. During that interval, the original device doesn't see the token being used so it send the token again. As it sends it, the 2nd device uses the token (3 msec late). Now the messages from the 1st and 2nd device clash. The 2nd device thinks it has the token and starts to use it. The 1st device thinks the token got lost and starts to poll for a new master. Messages clash, causing contention and eventually both devices recover to a valid state using the protocol rules. These rules require waiting various timeout periods. All the waiting, collisions and recovery waste time and bandwidth. If this happens often (as it will because one device doesn't meet the spec) then you can lose significant bandwidth.

Strategy

Capture Traffic using USB-485 converter
Use a tool like BACspy
Or
Use Hyperterminal
Analyze Traffic
Use a tool like BACspy online or Offline
Or
Perform a manual analysis


Configure HyperTerminal
Select the COM port which corresponds to your USB converter
Set the Baud Rate correctly
Set the other parameters as shown






Capture to File
Use this menu to start and stop the capture




As the messages are captured you will see these non-human readable characters fill the screen.





Inspect the captured data before you leave site to see if it usable.
You need a viewer capable of displaying the hex bytes. Here is a free download and hex viewer. Open the log file. 
To ensure you captured useful data look for messages that begin 55 FF. All BACnet MSTP messages begin with the same codes.
If you don’t see any then this may mean you captured at the wrong baud rate or some other setting is wrong. It is also possible that there is no BACnet communication.



You can use the CAS BACspy tool
BACspy automates this process of capture and analysis.

Friday 27 January 2012

How to Select (Filter) What you Capture with Wireshark

How To Capture With Wireshark

Before you start a capture you can specify a capture filter. The effect of the filter is to prevent all packets being captured. Doing this can save space when you save the log and it might make it easier to find the packets you are interested in. However, there is some risk that you might filter out the packets of interest.

 


For example, a BACnet device might not operate correctly because it is being hammered with packets from another protocol being sent incorrectly to the BACnet device. Our advise is to capture as much as possible and then filter what is displayed.



Here are some sample filters

Examples
Capture only traffic to or from IP address 172.18.5.4:
host 172.18.5.4
Capture only traffic to or from IP address 172.18.5.4 but exclude all FieldServer RUINET messages
host 192.168.1.81 and port not 1024
Capture traffic to or from a range of IP addresses:
net 192.168.0.0/24
or
net 192.168.0.0 mask 255.255.255.0
Capture traffic from a range of IP addresses:
src net 192.168.0.0/24
or
src net 192.168.0.0 mask 255.255.255.0
Capture traffic to a range of IP addresses:
dst net 192.168.0.0/24
or
dst net 192.168.0.0 mask 255.255.255.0
Capture only bacnet traffic: Assumes every device is compliant and is using the standard port.
port 47808 

Thursday 26 January 2012

The Energy Efficient Commercial Buildings Tax Deduction (CBTD)

According to the U.S. Department of Energy(DOE [http://www.energy.gov/]), lighting represents 40% of the average commercial building’s electric bill. While there are many different energy-efficient lighting solutions available with as much as a 45% return on investment. The initial cost of changing out the older lighting system is often cited as the main reason not to upgrade. Only 20% of existing commercial buildings feature some degree of upgraded lighting technology, while 80% continue to operate lighting systems installed before 1986. The Energy Efficient Commercial Buildings Tax Deduction (CBTD) was created to enhance the financial attractiveness of investment in the most energy-efficient lighting and other building technologies.

This special tax deduction allows building owners to write off the complete cost of upgrading a building’s indoor lighting, HVAC/hot water and building envelope in the year the new equipment is placed in service, capped at $1.80/sq.ft. Alternately, the owner could upgrade one of these three systems to earn the CBTD capped at $0.60/sq.ft. In short, with the CBTD, the cost of new lighting or other building systems can be claimed in a single tax year instead of amortized over a period of years.


What is the difference between a tax deduction and a tax credit?

Answer: The Commercial Building Tax Deduction is a tax deduction, not a tax credit. A tax credit is a direct dollar-for-dollar reduction of tax liability. A tax deduction is a cost subtracted from adjusted gross income when calculating taxable income; therefore, tax liability is not reduced dollar for dollar, but in proportion to the taxpayer’s tax bracket.
Many lighting projects result in tax deductions. Under current law, the cost of the new lighting must be capitalized and depreciated over time. Under the lighting rules in the CBTD, the owner can write off the entire expense of the new lighting, capped at $0.60/sq.ft., in the taxable year that the lighting is placed in service. So it is an accelerated tax deduction.Source: http://www.lightingtaxdeduction.org/CommercialBuildingsL1Q1.html

What types of buildings qualify?

Answer: The Commercial Buildings Deduction can be applied to any interior lighting project in any building that is within the scope of ASHRAE/IES Standard 90.1-2001 and is located in the United States, including privately and publicly owned buildings.
This includes public buildings, schools and rental housing. Rental housing must be within the scope of Standard 90.1-2001 and four stories or higher. Troubleshooting BACnet IP / Ethernet.
Religious buildings are covered by Standard 90.1-2001 but do not qualify for the deduction; they do not pay taxes, but they are not government buildings.

More information can be found here

Wednesday 25 January 2012

How to Find / Change A COM Port (Windows)


At certain times we need to figure out which device is connected to which COM port, so we can tweak the settings to our liking (such as changing the BAUD rate, switching the port to another one, etc…) or even for finding out which port you want to connect to.
In Windows, this very simple process will help you identify your COM port:

  1. Press Start on the start bar.
  2. Select Run…
  3. Enter “devmgmt.msc” and select Ok.



  1. Under the Device Manager window, expand the Ports category.
  2. Identify your devices.
  3. The COM port listed in the parentheses is the port you’re looking for.


To change the COM port the device is using, start with the steps listed above, then:

  1. Right-click the COM port.
  2. Click Properties.
  3. Select the Port Settings tab.
  4. Click Advanced.
  5. Change the COM Port Number by selecting a different port from the list of available ports.
  6. Click OK.
  7. Click OK on the Properties window.











The changes won’t show up right away (but they will take effect). If you restart Device Manager you’ll see the new assigned COM port. Article written by a system integrator.


Tuesday 24 January 2012

Thermal Insulation 101




There are 3 main ways that heat energy is transferred from one substance to another – convection, conduction and radiation. Thermal insulators retard these processes.

R-Value: A construction industry measure of a materials ability to resist thermal energy transfer.


Aerogel is an extreme insulator. Shown here, a thin slice of Aerogel stops wax crayons melting even though the blowtorch is pointing directly at it. Called a gel because of the way it is manufactured it presents itself as a light almost transparent solid with extremely high melting points, incredible R-values and ultra-low weight. It is reasonably strong. Strength, transparency and other mechanical properties are strongly affected by the manufacturing process. These insulators were used on the Mars Rover. An 18mm layer of aerogel will be sufficient to protect astronauts from temperatures as low as -130C. A sheet of Aerogel as a replacement for glass in a window provides 10-20 times the insulating power. “You could take a two- or three-bedroom house, insulate it with Aerogel and you could heat the house with a candle. But eventually the house would become too hot” – Dr Peter Tsou, Nasa JPL.

R-Values: 14 to +100
Weight : 3 times the weight of air.
Melting : 1200 °C (Silica Aerogel)
Starting to be used for skylights
AirGlass is a variant, similar to Aerogel ,used for window applications as an energy saver and as windows in firewalls.

Engineering Units - Watch Out you can easily be ripped off.
  • R-Value is not unit-less.
In the USA the common units are ft², °F, h/Btu.
The metric units are m².K/W
1 R value (USA) = 0.17611 m².K/W (SI Units)

  • R Values are calculated / published for a standard set of conditions such as constant temp and no air flow. Thus the published R-value and the effective R-value can be very different.
Aerogel Brand Names
These products are still expensive and some are hazardous to handle (nano particle dust).
Spaceloft = thin aerogel blanket/sheet made by Aspen Aerogels.

Common Insulators for Home and Commercial Buildings


Fiberglass batt
Completely useless at stopping air and moisture flow. Must be accompanies by air movement barrier. Installation quality sensitive.
Blown Fiberglass
Less sensitive to Installation quality. Check for cavities (how ?) Higher density means its better at stopping energy loss due to convection. Minimum wall cavity dimensions and non-self supporting limit applications.
Blown Cellulose
Similar to blown fiberglass. Densities are a little lower and R-value is lower. Made from flammable materials so must be treated.
Urethane Foam
R-value is stable in adverse weather conditions. Stable, self supporting. More expensive. Excellent at convective, conductive and radiation heat loss.
Studs – A huge waste of energy
The problem is that metal studs conduct heat many times faster than wood, serving as a sort of heat-loss superhighway. To prevent excessive heat loss, the studs must be properly insulated and sealed into the walls. The most commonly used and recommended solution is an exterior layer of rigid insulation sheathing to break that thermal bridge. But not all builders who use steel framing are addressing the alternative stud's shortcomings.


Wednesday 18 January 2012

Web Services Description Language

The purpose of this article is to provide a very brief description of the Web Services Description Language (or WSDL) as well as provide some resources of where to more detailed information and tutorials on the language.
WSDL is simply an XML file.  However, this file has a specific structure that can provide useful information to a user.  Specifically, WSDL is used to describe the functionality offered by a Web service.
This language is broken up into 5 parts, 3 of which (types, messages, and port type) are abstract definitions which define the interface, and the other 2 (binding and service) which are concrete details of how aforementioned abstract interfaces map to messages on the wire.
Very briefly, the 5 parts are described below:
  • Types – a container for abstract type definitions defined using XML Schema.
  • Message – a definition of an abstract message that may consist of multiple parts, each part may be of a different type.
  • PortType – an abstract set of operations supported by one or more endpoints; operations are defined by an exchange of messages.
  • Binding – a concrete protocol and data format specification for a particular PortType.
  • Service – a collection of related endpoints, where an endpoint is defined as a combination of a binding and an address (or URI).

These elements together make up a WSDL definition.


Resources

For more information on WSDL and Web Services please refer to these websites:

Tutorials
For some tutorials about WSDL and Web Services please refer to these websites: