The Beauty of Using BacNet Instance Numbers

During my work with Maurice on controlling a VFD with the T3000, I learned about Bacnet Instance numbers. Normally the control software references a Bacnet-IP address that contains the last octet of the VFD. (or whatever BacNet device you’re trying to read) But it turns out that every Bacnet device on the network has a unique “Instance Number”. Here are the advantages to using the instance number in your T3000 program.

    • The syntax is simpler. It’s referred to as just the instance number concatenated with the Bacnet AV,AI or AO and the Bacnet object number.
    • Finding the instance number is a snap with the T3000’s built-in Yabe (Bacnet Tool). All you have to do is explore your network with the tool and it will list the devices with their instance numbers in parentheses. Then just click on the list and you’ll see a list of all the device’s readable or writeable objects.
    • Finally, you can set all your Bacnet devices to use DHCP to assign their IP addresses on the fly. The instance number will be the same. (Maurice, please confirm this)

The ability to use instance numbers is a relatively new feature in the the T3000 software, so be sure to update your software and firmware

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Thanks for the patience as we got the feature working for you. Let us know how it goes when you start tying in those Carrier Bacnet chillers.



Will do, but I have to get my hands on the new T3-LB’s first. I was trying to wait patiently until the Shanghai office received the defective T3-BB, but I found out they’ve had it since 8/27. I am hoping they will reply to my email written earlier today.

Maurice, Guess I was not the only one interested in BACnet instances. I have updated to the most recent software and firmware today (Aug 24 and 47.6_8.23) and I still cannot get it to work properly. Fairly certain I have the syntax correct as programming shows no errors. Any assistance welcome.

Mike B.

Hope you don’t have the Asix processor version of the T3. It won’t read or write Bacnet objects. Learned that the hard way.


TDAWGTOO: The last remaining Asix based units were on sale at about half the usual price because they didn’t support MSTP (well), which we made pretty clear I think. They sold out fast.

MikeB: Email your program and send on some notes about your setup, Chelsea will check this over.


I have been trying to get this to work on a T3-BB with the ARM processor. I have two of the older Asix units as well. Thanks for the heads-up on that.

I just think it’s odd when the BACnet tool can see and read them but the T3 and T3000 can’t.



Think I have sent you all this before, but here it is again.

  1.   Block diagram of test setup to get thermostats working with T3-BB.
  2.   Control program for boilers, hot water, etc.
  3.   Test program for thermostats.

Chelsea has screen shots of the variables and network points screens for my system. It is only picking up the IP address instance of AI5, which would be INS33AI5, not the INS38AI5 that I want to read.


Asix based controllers kinda’ worked with MSTP but it wasn’t reliable. That was a big factor for switching to Arm though there’s other good things about it. There’s many bigger & better chips and tools with Arm.

Re instances:
Chelsea is continuing the work with you by email, checking your wireshark logs and various emailed notes and the program you just sent. The setup with your 3rd party bacnet wireless thermostats plus the 3rd party bacnet router is unique, we’re studying now and will get to the bottom of this.

Is there a way to change Object instance number? I would like to bring some logic to that numbers.

Yes of course, just connect and then edit the instance number in the t3000 graphical interface.

Maurice Duteau

I was trying to change CO2 sensor object instance, looks like In T3000 you can’t change it, but you can do it using Yabe ,by changing Analog_Value_6.

Good troubleshooting Andrius, we’ll add the instance number to the graphical UI for this product ASAP.

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