# Voltage Transducer

Discussion in 'General Electronics Chat' started by Tuck3rz, Nov 4, 2009.

1. ### Tuck3rz Thread Starter New Member

Nov 4, 2009
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May I know how does a Voltage and Current Transducer works and why does is it neccessary to connect it to a dual supplies?
What is the use of a additional R1 and Rm?
And what is the meaning of HT in the diagram.

Thank You

2. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
There will be a fixed ratio between the current that flows into the +HT/-HT terminals and the current that flows into or out of the the M (measure) terminal.

For this type LV 25-P the ratio secondary-to-primary Kn= 2.5:1 [2500:1000]

If the primary current is 10mA then the secondary (M terminal) current is 25mA.

The dual supply is (most probably) required to conveniently set the nominal secondary (M) current to zero for zero primary current. It's an intentional consequence of the unit's internal electronic design.

When the device is used as a voltage-to-current transducer, the resistor R1 limits the sensing current drawn from the voltage to be measured.

Suppose you want to measure a full scale DC voltage of 250V. To limit the primary current to 10mA you would need a resistance

R1=250/10mA-Rp = 25kΩ-250Ω=24.75kΩ

where Rp=primary resistance=250Ω [see the data sheet]

Rm is the sensing resistor in the M terminal used to convert the M terminal current Is into a sensible voltage. One side of Rm connects to the 0V terminal of the power supply - which can be conveniently set as the signal ground or reference. If Rm=100Ω in the example being considered, then the output voltage across Rm would be 25mA x 100Ω = 2.5V @ 250V on the high voltage side (@ 10mA primary current).

3. ### Tuck3rz Thread Starter New Member

Nov 4, 2009
17
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Is it appropiate to say that the dual supplies is use to power up the transducer?

4. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
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Yes - correct.

5. ### Tuck3rz Thread Starter New Member

Nov 4, 2009
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Ohhhh... Thanks alot bro for ur help =D

6. ### Tuck3rz Thread Starter New Member

Nov 4, 2009
17
0
May I know what is the meaning of galvanic isolation in a simple terms? I read the meaning at wiki but still not sure of the meaning still

7. ### Tuck3rz Thread Starter New Member

Nov 4, 2009
17
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How do you calculate Rm and R1 anyone cause i m not really sure the difference between them

8. ### SebyS New Member

Nov 22, 2010
1
0
Hi.
I use this voltage transducer (LV 25-P) and the following values for the resistances:
R1 = 22K 5W
Rm = 180
The problem is that R1 gets very hot when the applied voltage exceeds 200V. It is normal, or am I wrong somewhere ?
Thanks for the response.