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 thermostat. Our example is a simple device that has a temperature sensor, allows the set point to be changed locally or remotely, has a local remote selection and reports there is an internal fault by reporting its status as normal/abnormal.
Commonly used properties
Object Type: Popular Object Types: Analog Input, Analog Output, Binary Input, Binary Output.
Instance Number: A number that must be not be repeated for any other object of the same type.
Name: The optional property called ‘Description’ is usually used to describe the object. This porperty is often no more than a tag.
Present Value: The current value of the object. BACnet has ways of telling you if the present value is valid – it uses a property called ‘Reliability’.
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
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 writable and commandable properties and the conflict resolution only applies to commandable properties. For writable ( and non-commandable properties) the last write wins and overwrites any previous writes – there is no conflict resolution.
Which properties are commandable and how does the command resolution work ?
• The Present Value of AO, BO, MO objects are always commandable.
• The Present Value of AV, BV, MV objects are commandable if the vendor implemented them that way. It’s a vendor choice. You can tell what choice they made by looking for the Priority_Array and Relinquish_Default properties on the object. That’s a clue but not a guarantee (we have found). Last resort is their documentation. (good luck).
• A vendor may choose to make any vendor (proprietary) property commandable. If a property is commandable then it is required to have appropriately named Priority_Array and Relinquish_Default properties.
If an object has a Present Value that is commandable then it also has two additional properties ; Priority Array and Relinquish Default. These two properties are used to resolve command conflicts.
When a write is sent to a commandable point it always contains a priority. If the priority is not specified then the priority is assumed to be the lowest. There are 16 priorities. 16 is the lowest. On restart each slot in the array is set to a Null (unused) state. When the command is received the BACnet device updates the slot in the Priority Array that corresponds to the commanded priority with the new value.
The device continuously looks thru the priority array of each commandable property and looks for the highest priority slot that is non Null. It uses that value to update the Present Value. Now its easy to understand why the command you sent to an objects Present Value has no effect. You may have commanded with a priority lower than the one currently in use.
How to you empty a priority slot ? You send a command to the point to relinquish (give up control). This is like a normal command – its specifies a value ( a special value – Null ) and a priority. The device frees the Priority Array slot that corresponds to the relinquished priority. There are 3 possible outcomes to a relinquish – 1) There is no change to the Present Value because the relinquished priority is lower than the one in use 2) The Present Value changes because the relinquished command was at a higher priority than another commanded value. 3) All the Priority Array slots are now Null (unused). In this case the device uses the value of the Relinquish Default property to set the value of the present value.
What happens if two remotes device command at the same priority ? The last command wins, overwriting the value in the Priority Array for the given priority ? The same applies to relinquishing – the first relinquisher wins. How do you avoid this ? Assign different devices, application or functions different priorities. These choices are site specific. BACnet does names the priorities to suggest a use but how they are used is up to you – the implementor.
Some Objects that have commandable Present Values also have properties that define a minimum on and/or off time. When either of these are present it could affect the outcome of the write you send to the Present Value. A full description of this behavior will be provided in a subsequent article.
Worked Example:
The Relinquish Default Value is set by the device. The Vendor may choose to make it a writable property in which case in can be changed remotely. Even though the present value is commanded the device stores the commanded value in the priority array and uses the highest priority array slot to set the Present Value.
In our example, the device boots, the Priority array slots are all Null (Unused) and this vendor has set the Relinquish Default to 50. Since all the slots are null the device sets the Present Value to the Relinquish Default Value. The Present Value changes to 50.
Now a command is sent to set this objects Present Value to 45 at Priority 5. The device sets slot 5 in the Priority Array to 45. It then starts at the highest priority (1) and looks for the 1st non Null slot. It finds slot 5 filled with 45 and sets the Present Value to 45.
Now a new command is sent to set this objects Present Value to 70 at Priority 8. The device sets slot 8 in the Priority Array to 70 . It then starts at the highest priority (1) and looks for the 1st non Null slot. It finds slot 5 filled with 45. Thus there is no change to the Present Value to 45.
Now a command is sent to Relinquish the command at Priority 5. One would hope that the device that sent the original command sent the relinquish command but that is up to you and how you configured you system. When the relinquish command is received, the device sets the corresponding slot in the Priority Array to Null. The device then starts at the highest priority (1) and looks for the 1st non Null slot. The device finds slot 8 filled with 70. It changes the Present Value to 70.
The most recent command at a specific priority wins. Here a command is sent to set the Present Value to 80 at priority 8. The device overrides slot 8 in the array with the new value. In this case it is also the highest priority slot that is used so the device updates the Present Value to 80.
Finally, a command is sent to relinquish the command at priority 8. Slot 8 is set to Null and when the device looks through the priorty array it finds it all empty and it thus uses the Relinquish Default value to set the Present Value to 50.
This mechanism can be complicated if the object has minimum on/off times.
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
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 property values - they do work for us as data consumers. The rest is used to maintain the network - passing the token around and looking for new devices.
It’s not possible to provide a calculator to work out how many devices to install on a single network but the following list provides some help in assessing bandwidth considerations.
How many of the devices will be BACnet slaves.
Token passing and looking for new devices on the MSTP trunk consumes a fair amount of bandwidth.
A BACnet slave can be read/written but never gets token so it cant initiate any messages because it never gets the token. The more slave the fewer token passes. Typically you are not able to put a device in slave mode. Most vendors implement their devices as masters (ie token passing devices)
How many Objects in each device are you interested in monitoring ?
The more you read and the greater the frequency the more bandwidth that will be consumed.
It takes approx 30 bytes to poll for a single property. It takes about 40 bytes to reply. A token is 8 bytes as is a Poll for master.
Assume that 50% of your bandwidth will be used by overhead (token, poll for master).
Divide the baud rate by 10 to get bytes per seconds.
Using a number like 30+40=70 as a best case and 100 as a worst case (obviously reading descriptions will take more) multiply by the number of objects and properties you are going to poll on a regular basis.
Here are some typical numbers assuming device doesn’t support the ‘multiple’ services (see below).
How many properties from each of these objects ?
What is the baud rate?
What is Max Master Set to?
Every few cycles each (master) token passing device on the network must look to see if there are new devices. Max Master determines the biggest address that must be searched for. Each search involves sending a message and waiting for a response or a timeout (if the devices isn’t there). Timeouts cost time. The higher the number of Max Master (default is 127) the more potential devices must be searched for. If you use Max master to improve bandwidth then you must adjust it in each device.
Do the devices support the “Read/Write Property Multiple” services or must each property be read in a separate message?
Every few cycles each (master) token passing device on the network must look to see if there are new devices. Max Master determines the biggest address that must be searched for. Each search involves sending a message and waiting for a response or a timeout (if the devices isn’t there). Timeouts cost time. The higher the number of Max Master (default is 127) the more potential devices must be searched for. If you use Max master to improve bandwidth then you must adjust it in each device.
Obviously, if you can read a chunk of properties in one message you will be better off than if you can only read a single one.
Can you use BACNet’s COV mechanism?
COV stands for Change of Value. When a device supports COV another device / application can subscribe to receive notifications when an object property changes. This means the data client doesn’t have to poll for data continuously but can wait passively to be notified of the change. This reduces the number of messages on a network dramatically.
Some devices are slower than others.
BACnet allows up to 15 msec for a device to use the token. Since most messages on a MSTP network are token passes a device that uses the token in 5 msec will consume much less bandwidth than one that takes 15msec. (A number of vendors relax this requirement to allow for other vendors implementations. The more relaxed the more bandwidth is consumed doing nothing.)
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
(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 it is easy to understand the difference between a MSTP master and slave. A slave is a device that can only send responses. A master is an initiator of a service request.
Only allowing masters to initiate a message exchange when they have the token provides a mechanism whereby there can be multiple masters on a network and contention or collision can be avoided. Ethernet uses a different system – it allows collisions and provides a recovery mechanism. Imposing rules on the token passing such as specifying how much a master can do while it has the token provides a mechanism to balance the performance of various devices on a single network.
Back to the question of how new devices are added to the network. If you add a new slave device then you will need to program at least one master on the network to exchange data with that slave. The master needs to be programmed specifically to read that slave since slave devices don’t support discovery.(That’s one of the reasons that most field devices are not slave devices.)
If you add another master it needs to receive the token before it can act like a master but the other devices on the network need to discover the new device first. Every master on the network, has the job, of periodically polling for a new master.
Each master knows who the next master on a network is, because that is who it will pass the token to. So, each master, must poll for masters that could exist in the address range that exists between its own address and the next master’s address. Thus a master addressed as 1 must look for master’s in the range 2 to 10 if the next known master is 11. Master number 11 must look for new masters starting at 12 etc. The master with the highest number must try masters …,127,0…… When a device receives a poll asking if it is a master (Called a ‘Poll for Master’ message) it replies immediately. In the above example, if master number 1 cant find a master number 2 it should try number 3.
When should it try ? That’s a choice that is left up to the implementor of the BACnet protocol on that device. The spec only demands a minimum of 1 Poll for Master every 50 times a master receives or uses the token. The new master must respond within 20 milliseconds.
You can see, that if every master polls for a large number of new masters and they do this often then lots of bandwidth is lost. For this reason BACnet MSTP has a parameter called Max Master. Each master has its own setting for this variable. Typically it is set at 127 but imagine that master number 50 is the highest master on the network, and its Max Master is set to 64. Then it will never discover a new master whose address is larger than its max master, ie it will never discover master with address 65 to 127. This is a common reason why a new device on a network is not discovered.
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
Have you ever needed to snoop a RS232 serial port to observe the messages passing back and forth? It’s easier than you thought. All you need is application called HyperTerminal and the simple cable below. The cable can be assembled in minutes and requires a couple of diodes which you can probably buy for pennies. HyperTerminal is provided free with the Windows Operating System.
Here is what you need to do
1. Assemble the cable.
You need a 3 conductor cable and a 3 9-pin d-type connectors. We suggest you put a male on one end and a female on the other end and do not cross pins 2 and 3 over. That way you have a cable segment that will extend any cable without reuiring sex changes or worrying about 2-3 cross over. Put a female connector on the snoop end so it connects to your PC port without a sex change.
The Diode part number is 1N4148. The black band on a diode is the cathode end and corresponds to the vertical bar in the schematic of a diode.
A diagram is provided below the text of this article.
2. Connect
Connect the devices with your cable and connect the snoop to your computers serial port.
3. Run HyperTeminal
START, Programs, Accessories, (Communications), HyperTerminal
Set the port and configure it. In this example we use COM2 to snoop on a 9600,Even,8,1 conversation.
4. Capture Messages
In HyperTerminal, select the ‘Transfer’ menu.
Select Capture Text (even if the protocol you are snooping on is binary)
Specify a file name.
When you have captured enough, stop the capture and you can then use the file to view the conversations.
5. Limitations
No timing will be captured. All the messages sent and received by the devices you are snooping on will be ‘received’ only in HyperTerminal. This you will have to deduce the message ends/starts.
No timing information is available
If the messages are binary you will need to view the binary file in binary mode. You cant do this with notepad or WordPad. We use the Visual Slick Edit editor – Use Ctrl-Shift-H to change the view to binary.
ScreenShots
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
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 between its own MAC address and its next station.
For example
There are three devices on the network, 0×02, 0×03, 0×07.
All of the devices have a Npoll of 255, and have received the token 254 times since the start.
0×02 receives the token and increments its own TokenCount to 255. 0×02 now goes in to poll for master mode and attempts to find a new master, the NS (next station) just happens to be the PS (poll station) as well so TokenCount is reset to zero with out a poll for master message being sent out. 0×02 sends the token to 0×03.
0×03 receives the token and increments its own TokenCount to 255. 0×03 now goes in to poll for master mode and attempts to find a new master. It will poll for a new master between the range of 0×04-0×06. If it does not find a new master it will pass the token on to 0×07.
0×07 receives the token and increments its own TokenCount to 255. 0×03 now goes in to poll for master mode and attempts to find a new master. It will poll for a new master between the range of 0×08-Nmax_master then 0×00-0×01. But 0×07 has a Nmax_info_frames of 5 so it will only poll for 5 new master before it will pass on the token to 0×02. Next time 0×07 receives the token it will start to poll for a new master where it last left off at 5 frames a time.
Npoll
The number of tokens received or used before a Poll For Master cycle is executed: Default: 50.
Nmax_master
This parameter represents the value of the Max_Master property of the node’s Device object. The value of Max_Master specifies the highest allowable address for master nodes. The value of Max_Master shall be less than or equal to 127. If Max_Master is not writable in a node, its value shall be 127.
Nmax_info_frames
This parameter represents the value of the Max_Info_Frames property of the node’s Device object. The value of Max_Info_Frames specifies the maximum number of information frames the node may send before it must pass the token. Max_Info_Frames may have different values on different nodes. This may be used to allocate more or less of the available link bandwidth to particular nodes. If Max_Info_Frames is not writable in a node, its value shall be 1.
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
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 used when the token is sent out.
If the node that receives the token (NS) does not use the token before the previous stations (TS) Tusage_timeout the previous station (TS) will resend the token Nretry_token times before attempting to poll for a new master.
For example
If Tusage_timeout is set to 20 and Device A sends the token to Device B, device B has a total of 20 ms to use the token before Device A times out and sends the token again. This cycle will continue Nretry_token times. If Device B never responds in time then Device A will attempt to poll for a new master starting at Device B + 1 MAC.
I suggest that you increase the Tusage_timeout from 20 ms to something like 50-100 ms.
Must not exceed 100ms
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
TIA Telecommunications Industry Association, TIA defined standard TIA-568-B which defines the cables and structured or modular cabling systems and termination standards for building and telecom cabling systems.
Cat5 and Cat5e Cable – What is the difference?
Very simply put – The 5e cable is tested to a higher standard. A manufacturer may produce a single cable and only test some of it to the 5e standard. The physical characteristics of the cable are no different but the Cat5e’s higher specification makes it suitable for Gigabit Ethernet.
Whilst we are on the subject – what about Cat6 ? Bandwidth is 2.5 greater at 250MhZ and that’s probably the limit with RJ45 connectors. You might be future proofing using this cable but you could also be wasting money. Also remember that Cat6 is a high tech cable and requires connectors and patch cables assembled to meet the standard.
Category 5
Category 5e
Frequency
100 MHz
100 MHz
Attenuation (Min. at 100 MHz)
22 dB
22 dB
Characteristic Impedance
100 ohms ± 15%
100 ohms ± 15%
NEXT (Min. at 100 MHz)
32.3 dB
35.3 dB
PS-NEXT (Min. at 100 MHz)
no specification
32.3 dB
ELFEXT (Min. at 100 MHz)
no specification
23.8 dB
PS-ELFEXT (Min. at 100 MHz)
no specification
20.8 dB
Return Loss (Min. at 100 MHz)
16.0 dB
20.1 dB
Delay Skew (Max. per 100 m)
no specification
45 ns
Source : discountcablesusa.com
Below are comparisons of two cables – one a Cat5 and the other Cat5e.
Cat5e Cable Example
Part Number: 11700A Paired - Category 5e DataTuff® Twisted Pair Cable
DESCRIPTION:
24 AWG Bonded-Pairs solid bare copper conductors, polyolefin insulation, PVC inner jacket, rip cord, industrial grade sunlight- and oil-resistant PVC outer jacket. Sequential marking at two foot intervals.
CONDUCTOR :
Number of Pairs: 4
Total Number of Conductors: 8
AWG: 24
Stranding: Solid
Conductor Diameter: .020 in.
Conductor Material: BC - Bare Copper
INSULATION :
Insulation Material: PO - Polyolefin
Nom. Insulation Wall Thickness: .009 in.
Insulation Diameter: .035 in.
Pair Color Code Chart:
Number Color
1 White/Blue Stripe & Blue
2 White/Orange Stripe & Orange
3 White/Green Stripe & Green Number Color
4 White/Brown Stripe & Brown
INNER JACKET :
Inner Jacket Material: PVC - Polyvinyl Chloride
Inner Jacket Diameter: .200 in.
Inner Jacket Ripcord: Yes
OUTER SHIELD :
Outer Shield Material: Unshielded
OUTER SHIELD SEPARATOR :
Outer Shield Separator Thickness: 0.001 in.
OUTER JACKET :
Outer Jacket Material: Industrial Grade PVC - Polyvinyl Chloride
Outer Jacket Nominal Wall Thickness: .035 in.
Outer Jacket Ripcord: Yes
OVERALL NOMINAL DIAMETER :
Overall Nominal Diameter: .285 in.
MECHANICAL CHARACTERISTICS :
Operating Temperature Range: -40°C To +75°C
Storage Temperature Range: -40°C To +85°C
Installation Temperature Range: -25°C To +75°C
Bulk Cable Weight: 35 lbs/1000 ft.
Max. Recommended Pulling Tension: 40 lbs.
Min. Bend Radius (Install): 0.29 in.
APPLICABLE SPECIFICATIONS AND AGENCY COMPLIANCE :
APPLICABLE STANDARDS :
NEC/(UL) Specification: CMR, CMX-Outdoor, UL444
CEC/C(UL) Specification: CMR
IEC Specification: 11801 Category 5
EU RoHS Compliant (Y/N): Yes
EU RoHS Compliance Date (mm/dd/yyyy):: 01/01/2004
PMSHA Specification: P-07-KA060005
TIA/EIA Specification: 568-B.2 Category 5e
Other Specification: NEMA WC-63.1 Category 5e, Ethernet/IPâ„¢ compliant, UL verified to Category 5e
FLAME TEST :
UL Flame Test: UL1666 Riser
CSA Flame Test: FT4
SUITABILITY :
Suitability - Indoor: Yes
Suitability - Outdoor: Yes
Sunlight Resistance: Yes
Oil Resistance: Yes
PLENUM/NON-PLENUM :
Plenum (Y/N): N
ELECTRICAL CHARACTERISTICS :
Nom. Mutual Capacitance @ pF/ft
Maximum Capacitance Unbalance (pF/100 m): 66 pF/100 m
Nominal Velocity of Propagation: 70 %
Maximum Delay (ns/100 m): 510 ns/100 m
Maximum Delay Skew (ns/100m): 25 ns/100 m
Maximum Conductor DC Resistance @ 20 Deg. C: 9 O/100 m
Maximum DCR Unbalance @ 20 Deg. C: 3 %
Max. Operating Voltage - UL: 300 V RMS
ELECTRICAL CHARACTERISTICS - PREMISE :
Premise Cable Electricals Table 1:
Frequency (MHz) Max. Attenuation (dB/100 m) Min. NEXT (dB) Min. PSNEXT (dB) Min. ACR (dB) Min. PSACR (dB) Min. Return Loss (dB) Min. Structural Return Loss (dB)
1 2.0 65.3 65.3 63.3 63.3 20.0
4 4.0 56.3 56.3 52.3 52.3 23.0
8 5.7 51.8 51.8 46.1 46.1 24.5
10 6.4 50.3 50.3 43.9 43.9 25.0
16 8.1 47.3 47.3 39.1 39.1 25.0
20 9.2 45.8 45.8 35.2 35.2 25.0
25 10.3 44.3 44.3 34.1 34.1 24.3
31.25 11.6 42.9 42.9 31.3 31.3 23.6
62.5 16.8 38.4 38.4 21.6 21.6 21.5
100 21.7 35.3 35.3 17.1 17.1 20.1
155 27.7 32.5 32.5 4.7 4.7 19.0
200 32.0 30.8 30.8 3.0 3.0 19.0
250 36.4 29.3 29.3 >0 >0 18.0
300 40.5 28.2 28.2 >0 >0 18.0
310 41.3 27.9 27.9 18.0
350 44.3 27.2 27.2 17.0
Premise Cable Electricals Table 2:
Frequency (MHz) Input (Unfitted) Impedance (O) Fitted Impedance (O) Min. ELFEXT (dB) Min. PSELFEXT (dB)
1 100 ± 12 105 ± 10 63.8 60.8
4 100 ± 12 100 ± 10 51.7 48.7
8 100 ± 12 100 ± 10 45.7 42.7
10 100 ± 12 100 ± 10 43.8 40.8
16 100 ± 12 100 ± 10 39.7 36.7
20 100 ± 12 100 ± 10 37.7 34.7
25 100 ± 15 100 ± 10 35.8 32.8
31.25 100 ± 15 100 ± 10 33.9 30.9
62.5 100 ± 15 100 ± 10 27.8 24.8
100 100 ± 15 100 ± 10 23.8 20.8
155 100 ± 18 100 ± 10 19.9 16.9
200 100 ± 20 100 ± 10 17.7 14.7
250 100 ± 20 100 ± 10 15.8 12.8
300 100 ± 20 100 ± 10 14.2 11.2
310 100 ± 20 100 ± 10 13.9 10.9
350 100 ± 22 100 ± 10 12.9 9.9
Cat5 Cable Example
Part Number: 1633A Paired - Category 5 Unbonded-Pair Cable
DESCRIPTION:
24 AWG solid bare copper conductors, non-plenum, Polyolefin insulation, twisted pairs, overall Beldfoil® Shield, drain wire, rip cord, see color code chart (below), PVC jacket (gray or blue).
SUITABLE APPLICATIONS :
Suitable Applications: Premise Horizontal Cable
PHYSICAL CHARACTERISTICS :
CONDUCTOR :
Number of Pairs: 4
Total Number of Conductors: 8
AWG: 24
Stranding: Solid
Conductor Material: BC - Bare Copper
INSULATION :
Insulation Material:
- Polyolefin
>Pair Color Code Chart:
Number Color
1 White/Blue Stripe & Blue
2 White/Orange Stripe & Orange
3 White/Green Stripe & Green
4 White/Brown Stripe & Brown
OUTER SHIELD :
Outer Shield Material Trade Name: Beldfoil®
Outer Shield Type: Tape
Outer Shield Material: Aluminum Foil-Polyester Tape
Outer Shield %Coverage: 100 %
OUTER SHIELD DRAIN WIRE :
Outer Shield Drain Wire AWG: 24
Outer Shield Drain Wire Stranding: Solid
Outer Shield Drain Wire Conductor Material: TC - Tinned Copper
OUTER JACKET :
Outer Jacket Material: PVC - Polyvinyl Chloride
Outer Jacket Ripcord: Yes
OVERALL NOMINAL DIAMETER :
Overall Nominal Diameter: .260 in.
MECHANICAL CHARACTERISTICS :
Operating Temperature Range: -20°C To +80°C
Bulk Cable Weight: 28 lbs/1000 ft.
Max. Recommended Pulling Tension: 25 lbs.
Min. Bend Radius (Install): 1 in.
APPLICABLE SPECIFICATIONS AND AGENCY COMPLIANCE :
APPLICABLE STANDARDS :
NEC/(UL) Specification: CM, UL444
CEC/C(UL) Specification: CM
EU CE Mark (Y/N): Yes
EU RoHS Compliant (Y/N): Yes
EU RoHS Compliance Date (mm/dd/yyyy):: 01/01/2004
TIA/EIA Specification: 568 TSB 36, Category 5
Other Specification: UL verified to TSB 36, Category 5
FLAME TEST :
UL Flame Test: UL1685 UL Loading
CSA Flame Test: FT1
PLENUM/NON-PLENUM :
Plenum (Y/N): N
ELECTRICAL CHARACTERISTICS :
Nom. Mutual Capacitance @ pF/ft
Maximum Capacitance Unbalance (pF/100 m): 330 pF/100 m
Nominal Velocity of Propagation: 67 %
Maximum Delay (ns/100 m): 538 @ 100MHz ns/100 m
Maximum Delay Skew (ns/100m): 45 ns/100 m
Maximum Conductor DC Resistance @ 20 Deg. C: 9.38 O/100 m
Maximum DCR Unbalance @ 20 Deg. C: 5 %
Max. Operating Voltage - UL: 300 V RMS
ELECTRICAL CHARACTERISTICS - PREMISE :
Premise Cable Electricals:
Frequency (MHz) Max. Attenuation (dB/100 m) Min. NEXT (dB) Min. PSNEXT (dB) Min. Structural Return Loss (dB) Fitted Impedance (Ohms)
1 2.0 62.3 No Spec No Spec 100 ± 15%
4 4.1 53.3 No Spec No Spec 100 ± 15%
8 5.8 48.8 No Spec No Spec 100 ± 15%
10 6.5 47.3 No Spec No Spec 100 ± 15%
16 8.2 44.3 No Spec No Spec 100 ± 15%
20 9.3 42.8 No Spec No Spec 100 ± 15%
25 10.4 41.3 No Spec No Spec 100 ± 15%
31.25 11.7 39.9 No Spec No Spec 100 ± 15%
62.5 17.0 35.4 No Spec No Spec 100 ± 15%
100 22.0 32.3 No Spec No Spec 100 ± 15%
Straight Thru Patch Cable vs Cross-Over Cable
The easiest way to tell the difference is to take the two ends and gold them up against each other. If the same color wires on are the same pins it’s a straight through path cable. If any of them cross-over then it’s a ….. cable.
Ethernet Cable Color Coding
There are two color coding standards. The color coding standard does not affect whether the cable is a cross-over or straight through patch cable. Color does not affect performance or use of the cable.
Standard 568A
Standard 568B
This is the most commonly used for patch cables.
1
White-Green
1
White-Orange
2
Green
2
Orange
3
White-Orange
3
White-Green
4
Blue
4
Blue
5
White-Blue
5
White-Blue
6
Orange
6
Green
7
White-Brown
7
White-Brown
8
Brown
8
Brown
Why twist the pairs ?
Signals can bleed or crosstalk from one pair to another. Twsisting significantly reduces the degree of crosstalk.
Near End Cross Talk is known as NEXT
Far End Cross Talk is known as FEXT
Ethernet Cables and RJ45 Connectors
It is often recommended that the RJ45 connector match the cable – If the cable is stranded the use a RJ45 plug with stranded conductors. The author cant find a reason for this assertion.
The standard for the use of RJ45 connectors on cat5 and Cat5e cable is a maximum untwist of 0.5inch for termination on the RJ45 connector.
Under no circumstances should an other part of the cable be unwound. Take great care in assembling cables and inspect the assembly if the cable doesn’t perform well.
Stranded vs Solid Conductors
The use of stranded conductors is recommended for flexible cables like patch cable. There is some discussion suggesting that solid conductors offer slightly better performance over the life of the cable.
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
BACnet clients must respect the servers report of supported services
In BACnet when a client connects to a server it has the responsibility of enquiring what services the server supports and then only using the supported services. In BACnet a server should be driven to a failed state if it receives a message requesing a service that isnt supported.
There are always grey areas in specs. Despite the plugfests, despite the testing … there will always be little gotcha’s. Isnt that why there are plugfests in the 1st place.
We recently supported a site where the server device reported that it did not support COV. Despite this ,the Andover Continuum software sent COV subscription requests. This caused a failure on the server device which was not able to handle them correctly.Normally the Andover Continuum respects the service capability of the server device but in this case additional programming had been configured in a program block which used subscriptions. These program blocks appear in this configuration not to have checked the supported services list before using one. Normally the server device responds to requests for unsuported services correctly - with an rejection message.
The problem was hard to diagnose for the following reasons;1. The problem manifested itself by allowing one server device to be recognized and its points were seen but when an identical (except for device instance id) was added then both servers failed.2. An attempt was made to emulate the problem offsite. The same controller and software version were used. The offsite test did not use the same configuration. Offsite , we were able to bring in the service devices and see the points. However, there were no program blocks and thus the problem did not show up.3. We obtained communication logs from site. The logs did show problems but these were a manifestation of the failure in the service devices caused by the COV subscription. Thus these errors were red herrings.4. The subscription message is sent early after the system is reset. Thus the subscription message was not captured in the logs.
Conclusions;
It is probable that this same problem exists in all versions since 1.73 since we have not seen a correction notice.
There is no substitute for capturing full logs from a site. Logs should be captured using external devices to avoid placing any additional load on the devices already installed on the network.Using an external device can be as simple as using a USB-485 converter. Chipkin Automation System has software tools for capturing BACNet MSTP logs. They are available free of charge. Call or email us for a free copy.
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
