Maximum/Recommended number of BCPM monitored by one Com'x 510

[Jan]

Hi everyone,

Can someone help with a recommended/maximum number of BCPM (branch circuit power monitors) that can be monitored by a single Com'x 510 ? 

(I attached some example of the monitored device.) The customer has currently 10 BCPMs monitored by a single Com'x 510 but the unit/web interface is very slow, not loading sensor values properly. 

Thank you,

Jan

[Jan]

Adding example of BCPM device.

[KuanKhoon · Accepted solution]

Hi,

I'm assuming that your BCPM is 42-ways and not the 84 ways version and it is connected at the RS-485 port using 2-wire Modbus RTU directly to the Com'X510.

First, 10 pieces of BCPM is way too much information that the Com'X 510 can handle reliably. Each BCPM board will generate 6 x voltage readings and 1 frequency reading while each channel will generate current, power, power factor and energy value to say the least. Even if you just simply log just the energy and power readings, it would be 84 pieces of information per BCPM. Multiply that by 10 and you have 840 pieces of information. I have maxed out the Com'X 510 at around 100+ readings across multiple devices, so what you are experience is not unexpected.

Second, BCPM is not exactly a "fast device". The RS-485 connection at best is 38400 baud (limited by the Com'X 510) and with large amount of data to be transferred (refer to the paragraph before), result in a relatively slow poll and respond type of behaviour. RS-485 is a master and slave type of communication, master talks, slave respond, the rest waits for their turn. 10 devices plus the fact that each device takes time to repond results in overall sluggish response. Also, expected.

Third, RS-485 line termination. This cannot be over emphasised that any RS-485 connection (regardless of how short/long/twisty/good/bad) must be terminated with a resistor of a value matching that of the intrinsic impedance of the cable. This prevent end reflections that will FURTHER slow the already sluggish connection mentioned in second point. Make sure your connections are next to perfect in order to stand a chance. Ensure the line termination and line biasing is turned on at the Com'X 510 (assuming the Com'X is the last/first device in the chain).

Overall, I from experience, I would say to limit the Com'X 510 to a very conservative 1 x 84-way BCPM or 2 x 42-way BCPM in order to keep performance to an acceptable level. Limit your logging of the readings to energy only and at default 15 minutes interval.

[Jan]

Hi, 

Thank you for your help/advice on this. Your assumptions were correct; at the time, after doing some research on this and consulting with colleagues I recommended a solution along the lines of what you recommended above. It would have been great and helped a lot if someone would have replied to the post a bit earlier 🙂

Thank you again and have a nice day.