Current Clamp sensors with T3E-6CT

Hi,

I’m using a T3E-6CT GPIO module with current clamp sensors ( CS-SP-50A-DC ) connected to the Analog Input ports of the T3E-6CT. Using the T3000 software, I am able to read the current clamp sensor’s output voltages on the T3000 GUI and also using Modbus Poll application. I would like to continue using the Analog Input ports on the T3E-6CT (13 in number) and refrain from using the CT Input ports (only 6 in number).

( Sensor output voltages are between 0.03 - 0.09 V for an appliance rated for 2.5 A, when jumper position on the sensor is set to 10 A range. )

A few questions:

  1. Does changing the range from ’ 0 - 5 V ’ to ’ 0 - 100 Amp ’ on the ‘Inputs’ page using the T3000 software automatically convert the sensor output voltage value and give an accurate reading for current?

  2. How do I convert the obtained output DC voltage values to current? ( Kindly provide the calculation involved )

  3. Is there a shunt resistor present inside the sensor? If yes, kindly provide the value of the shunt resistance.

  4. Is there any scaling factor involved when changing the jumper position on the sensor? If yes, kindly provide the calculation involved.

Thank you in advance.
Any help would be greatly appreciated.

Regards,
Pranav

Thanks for your efforts with the T3E-6CT. Here’s a few notes that I think answer your questions.

The range setting of the T3000 will let you tailor the analog signal to your typical sensors: thermistors, dry contacts, analog sensors. In the case of a CS series current sensor, the output is 0-5V full scale.
Here’s the steps to build up a custom table for the current sensor. You only need to enter two points in the table, the min and max voltage and current values as shown at Tab4. Be sure to set the signal type at Tab5 to 0-5V.

As for accuracy, the current sensors are rated at a few percent and the performance is not great at low current readings due to the voltage drop across the onboard diodes (D1 in the schematic). You can increase the sensitivity (at the expense of reduced range) by wrapping the conductor through the sensor a few times. Then you would scale your custom table, divide the max value by the number of wraps.

There is a shunt resistor inside the unit, you can check the values in the schematic. Its been a while since we did this so I dont actually see which one is the ‘load resistor’ but you could measure with it with an Ohm meter, no current flowing and no connections to the controller.

The jumper on some models will set the full scale from 10A to 20A and I believe there’s 50A and 100A on some models. The value for each jumper position is on the sticker of the sensor.

1 Like

Hi,
Thank you for your quick response.

Just to confirm, internally in the T3000 software, is the output voltage value converted to current value in the following manner?

5 V → 10 Amps ( assuming sensor range is set to 10 A )
And so,
‘x’ V → (10 / 5) * ‘x’ Amps

Thanks in advance.

Regards,
Pranav

The custom table is a straight line from the minimum to the maximum data points. The controller can interpolate any voltage in between the min and the max to arrive at the reading in amps.

Also note: The minimum value doesn’t need to be at 0V, it could be at say, 0.7V which you could determine with some testing. That would improve your accuracy somewhat.

~WRD255.jpg

Hi,

Thank you for your response.

I’ve received a new set of current clamp sensors (CT-SP-XX-330mV, where XX - 1A, 5A, 10A and so on). The above mentioned current clamp sensor produces an output signal from 0 to 330 mV ac, proportional to the current.
( Note: I’m currently working on a project that involves reading Modbus registers of the T3E-6CT to obtain the current / output voltage readings of the current clamp sensors using small embedded boards. And so, I require to perform the output voltage to current value conversion programmatically. )

A few questions:

  1. Should the CT-SP-XX-330mV current clamp sensors be connected to only CT input ports of the T3E-6CT GPIO module? Would there be any change if the current sensors are connected to the AI ports ?

  2. On connecting the current clamp sensors to the CT input ports of the T3E-6CT, are the output signals of the sensor converted to current values (Amps) and stored by default in the Modbus registers by T3E-6CT? Or is there any user configuration to be performed using the T3000 software (example: setting the range to '0 - 100 Amps ’ ) ?

  3. For the CT-SP-XX-330mV sensors, should I setup a custom table ( a straight line, min value: 0 V and max value: 330 mV ) and calculate the corresponding reading in Amps? ( similar to the method employed for the CS-SP-50A-DC current sensors)

Thanks in advance.

Regards,
Pranav

  1. The 330mv signal is an AC signal which needs some signal conditioning which is available only on the 6 special CT inputs of the device. The remaining inputs are for thermistors, dry contacts and 0-10V transducer signals. They will not work with 330mvAC signals.
  2. Use the T3000 software to configure the range of the signal, you can search this forum for ‘custom tables’ and you’ll see how to do that.
  3. Yes, use the custom tables and configure the upper and lower amp readings depending on your CT

Final note: Use the T3000 → tools → register viewer to see the register numbers, descriptions and the current value. Once you are done setting up your modbus polling you don’t need to use T3000 any longer. It is just helpful during the initial integrating and setup.

~WRD255.jpg