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:
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?
How do I convert the obtained output DC voltage values to current? ( Kindly provide the calculation involved )
Is there a shunt resistor present inside the sensor? If yes, kindly provide the value of the shunt resistance.
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.
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.
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.
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:
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 ?
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 ’ ) ?
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)
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.
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.
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.
I’m currently working with the T3E-6CT GPIO module and current clamp sensors CT-SP-XX-330mV.
Also, I have a signal generator using which I attempted to simulate the output generated by the CT sensors.
From the documentation, I understand that the rated output for the CT sensor is 0.333 Vac, which means that a full scale output from a CT sensor should yield a 333 mV AC signal.
Tests performed:
Using the signal generator, I applied a 330 mV @ 60 Hz AC signal to a CT port on the T3E-6CT. I expected a full scale output of ‘100’ ( or 99 ) on the T3000 software when the range is set to ‘0-100A’. However, we get a value in the range ‘34’ - ‘36’.
When a 1 V @ 60 Hz AC signal is applied to the CT ports, we obtain a full scale output of ‘100’ on T3000 software.
Questions:
What is the conversion factor from CT sensor voltage to the output value shown in the Modbus register?
Since we are using CT sensors of varying ranges ( 1 A, 5 A and so on), we want to avoid setting up custom tables for each sensor range. We wish to obtain the output voltage from each CT sensor and perform further calculation/conversion using code. Considering this, is there any range setting ( or any other setting ) on the T3000 software that will store the raw output voltage value generated by CT sensors in Modbus registers? If so, what voltage value will be stored in the registers : Vpeak-to-peak or Vrms ?
You went to a lot of effort there and we’ll do our best to help out. Could you show us a view of the input configured as viewed from T3000. Specifically I would like to see the range setting and value of the current, just to confirm the range is set correctly.
Update: You could use the custom analog range if you are having trouble to get the signal to match the value. This is normally for creating ranges which are not included in the standard ranges, what you describe above is probably somethign else but just passing this on as a possible workaround.
Thank you for your suggestions regarding using a custom analog range. I’ll try that approach and get back to you.
Please find attached the required screenshots of the T3000 software ( inputs page ) and Modbus Poll software ( CT 1 registers ). We applied a 330 mV @ 60 Hz AC signal input to the CT 1 port of the T3E-6CT. We receive a value of 35.55 as shown in the screenshot.
Is there any way to store the output AC voltage value of the CT sensor in the Modbus registers?
Please let me know if you require any additional information.
Thank you.
Regards,
Pranav
T3000 software ( Inputs page - AC voltage input applied to CT 1 ):
You have done everything correctly but its our user interface which could have been more helpful. I think what this built in 100A range is assuming a 0-10V signal, we will add that to our user interface to avoid confusion. If you were to use Range50 and build a custom table it will be a better approach.
