Interfacing the HE055T01 hall effect current sensor to a WiSense node

I want to use a small network of WiSense nodes to measure the output the solar panels installed on the roof of my house. I have 8 panels producing 2 KW peak (8 * 250 Watts). The 8 panels are arranged in two strings of 4 panels each.  I needed a current sensor to measure the current output of each string. The HE055T01 is a high quality current sensor manufactured by Electrohms in Bangalore. It can be used to measure both AC and DC currents up 50 Amps. The HE055T01 has just three terminals.

  • Terminal #1 – Postive supply
  • Terminal #2 – Negative supply return.
  • Terminal #3 – This terminal outputs a current in proportion to the measure current (1 mA per Ampere of measured current).

This sensor requires two separate power supplies (one will be the positive supply and the other will be the negative supply). The negative supply allows the sensor to measure AC currents and the direction of DC currents. he055t01_bd

The HE055T01 outputs a current (through the burden resistor) directly proportional to the current being measured (let us call it primary current).  The sensor’s conversion ratio (as specified in the datasheet) is 1000:1. This means if the primary current is 1 Amp, the HE055T01 will output 1 mA through the burden resistance. If the primary current is 50 Amps, the HE055T01 will output 50 mA through the burden resistance. The HE055T01’s output current (Is) can be determined by measuring the voltage drop across the burden resistance. The primary current is then simply (Is * 1000) Amps. The MSP430G2955 microcontroller on a WiSense node has a channel 10 bit ADC module. I used channel #0 (Pin A0 / P2.0) to measure the voltage across the burden resistance. I used a burden resistance of 70 ohms. When output current is 50 milli-amps (corresponding to primary current of 50 Amps), the voltage across the burden resistance will be 3.5 Volts. I decided to use the ADC10 internal 2.5V reference voltage. To support measurement of high currents, I decided to use an op-amp to divide the ADC input voltage by 2. I wired up a circuit and was able to successfully transmit primary current values to a laptop via an LPWMN coordinator. In this setup I was measuring the current value every second.

he0 55t01_bd_wisense.

.

.

.

.

.

.

.

.

.

.

.

The figure above shows how the sensor is interfaced to  WiSense node.

20150127_143655

This pic (above) shows the HE055T01 sensor with two turns of the wire (caarrying the primary current) going through the sensor’s center.

20150127_143701

.

.

.

.

.

.

.

.

.

.

This pic (above) shows the rig used to test the sensor (interfaced to a WiSense node).

The node is configured as a full functioned device (FFD). The instrument in the background is a DC current generator. The white proto board next to the WiSense node has a 12 V -> 3.3 V regulator and the op-amp div by 2 circuit. Two 12V wall adapters are used to provide the two supplies needed by the HE055T01. The test rig was able to accurately measure the current output of the DC current generator and transmit the measurements once per second to a laptop to which a WiSense coordinator was connected. Now I need to put all the electronics in a weather proof enclosure and measure the output of the panels on my roof. Stay tuned for more updates. References:

Posted on January 29, 2015, in Uncategorized. Bookmark the permalink. Leave a comment.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: