Reverse current

[kdm7]

Hi,

I am using a lem lts 6-np current sensor. I am able to get calbrated positive current. But, my problem is that I am not able to get negative current values on my front panel (after reversing the terminals). 

[GerdW]

Hi kdm,

why do you think you need to "reverse" any terminals?

Why don't you stick with your original thread?

Why don't you provide your VI to analyze the problem?

How did you connect your LEM sensor? Which input pins?

How did you "reverse" terminals?

Why don't you read the sensor's spec sheet to know how to measure negative current?

After 100 posts to this forum you really should have learned to provide all information needed to answer your questions…

[kdm7]

Hi Gerd,

I am reversing the terminals of the current supplier to see if my VI can measure negative current. By the way the lem sensor's range is + or - 19A.

This is a different problem, so I started a new thread.

Sorry, I cannot provide my VI, it is confidential.

[GerdW]

Hi kdm,

I am reversing the terminals of the current supplier to see if my VI can measure negative current.

To reword it: you reversed the current flow through your LEM sensor at it's current input pins?

So you should read some voltages at your USB6008-AI. Which value(s) do you read? Which values did you read before reversing the current flow?

I cannot provide my VI, it is confidential.

What is confidential in an example VI containing just an DAQmx AI task reading values from an USB6008-AI pin and converting the voltage back to current values as is described in the sensor spec sheet?

Ok, so I will propose a confidential example VI:

[JB]

As mentionned in the datasheet, the output voltage of the LTS 6-NP is 2.5±(0.625*Ip/Ipn).

Ip = primary current

Ipn = primary nominal current, 6A for this type

So, for example :

• 0A : 2.5V
• 6A : 3.125V
• -6A : 1.875V

There is no need to reverse the wiring.

[kdm7]

Hi Gerd,

Yes, I reversed the current flow.

Before reversing : 1.3A , 1.43703V (This is correct)

After reversing: Voltage = 0.75V , I'm not sure about the current (I'm at home now.. I think -14.23..A ) ,But the multimeter reads -1.2A. The VI is supposed show -1.2A.

[GerdW]

Hi kdm,

we are talking about the LEM LTS 6-NP?

Then we need to calc:

Before reversing : 1.3A , 1.43703V (This is correct)

reading 1.437V means (1.437V-2.5V)*6A/0.625V =  -10.205A

After reversing: Voltage = 0.75V

same calculation: (0.75V-2.5V)*6A/0.625V = -16.8A

What do we learn from this calculation:

- You're still not able to read the spec sheet of your sensor.

- You surely wired this sensor wrong as you read voltages far away from expected values.

When measuring 1.25A your sensor should output either 2.37V or 2.63V, depending on current flow direction.

READ THE SPECS!

YOU DON'T NEED TO REVERSE THE CURRENT FLOW BY REWIRING!

[JB]

Assuming that the current is the same, the output voltage of the LEM can't be below 2.5V in both cases by reversing the wires. Something is wrong.

We all loose our time if you don't read our answers. Reading its datasheet carefully will really help you to understand how this module works.

[kdm7]

Hi Gerd,

Sorry, those were current readings (without and with error) (Before reversing values which I had posted)

I did use that formula. I don't remember the voltage value. But I checked with the multimeter, it was correct.

I noted down readings after reversing current flow.

After reversing: Voltage = 0.75V

calculation: (0.75V-2.5V)*6A/0.625V = -16.8A

My VI shows around -16.8A.. BUT I am actually supplying  -1.2A (As shown by multimeter) So I guess the Vout itself is wrong. But how and why?

[GerdW]

Hi kdm,

So I guess the Vout itself is wrong. But how and why?

We already discussed about attaching your "super confidential" VI.

I guess you either mis-wired the sensor or mis-wired the scaling logic in your VI. Go look for yourself…