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FMCC EUROPE
Components and technical solutions for power electronics
Calculation guide
Electronic technology current sensors
NCS sensors
1 - Reminder of the key elements
The supply voltage does not have any influence on the output signals.
2.1 - What load resistance (RM) is required to obtain a 5V measuring (VM = 5V) when the current IP = 6000A peak?
The measured current is greater than IPN (2000A for a NCS125-2), IS2 is therefore used as the measuring signal. Firstly the output current on IS2 must be calculated when IP = 6000A d.c.
IS2 = IP / IPMAX x ISMAX = 6000 /10000 x 20 = 12mA (correct because IS2MAX = ±20mA d.c.)
Now determine the value of the resistance RM
RM = VM / IS2 = 5 / 0,012 = 416,67Ω
Conclusion:
The NCS125-2 sensor can measure a 6000A peak on the signal output IS2 with a resistance of 416.67 Ω (greater than 350 Ω) because the output current is smaller than ISMAX i.e. 20mA d.c..The product of RM x ISMAX must always be smaller than or equal to maximum output of 7V d.c..
3 - Measurement circuit calculation (voltage output)
No special calculation needs to be made. This NCS sensor range supplies a voltage directly proportional to the primary current IP between -10V and +10V. A load resistance of a value greater than or equal to 10kΩ adapts the impedance of the measured output (VS1 or VS2) to the acquisition system.
Electronic technology current sensors
NCS sensors
1 - Reminder of the key elements
| Formulas: | Abbreviations | |
 | VM2 = RM2 x IS2 VM1 = RM1 x IS1 with 0Ω < RM1 or Rwith 0Ω < 350Ω | IP : primary current IPN : nominal primary current IPMAX : nominal primary current IS1 : secondary current at IPN IS2: secondary current at IPMAX VS1 : secondary voltage at IPN VS2 : secondary voltage at IPMAX VA : supply voltage VM : measuring voltageRS : resistance of the secondary winding RM : measuring resistance RMMIN : minimum measuring resistance RMMAX : maximal measuring resistance |
Reminder of the sensor electrical connection
2 - Measurement circuit calculation (current output)
Example with NCS125-2 sensor
| IPN = 2 000A | IS1 @ IPN = ±20mA |
| IPMAX = 10 000A | IS2 @ IPMAX = ±20mA |
| RM = 0 - 350Ω (IS1 & IS2) | VS1 @ IPN = ±10V |
| RM > 10kΩ (VS1 & VS2) | VS2 @ IPMAX = ±10V |
| VA = ±15V ... ±24V |
| The design of the sensor requires that 2 operating points are respected on the outputs IS1 and IS2: • A maximum measuring voltage of 7V d.c. (VMMAX ≤ RMMAX x ISMAX) • A maximum output current of ±20mA d.c.. |
The supply voltage does not have any influence on the output signals.
2.1 - What load resistance (RM) is required to obtain a 5V measuring (VM = 5V) when the current IP = 6000A peak?
The measured current is greater than IPN (2000A for a NCS125-2), IS2 is therefore used as the measuring signal. Firstly the output current on IS2 must be calculated when IP = 6000A d.c.
IS2 = IP / IPMAX x ISMAX = 6000 /10000 x 20 = 12mA (correct because IS2MAX = ±20mA d.c.)
Now determine the value of the resistance RM
RM = VM / IS2 = 5 / 0,012 = 416,67Ω
Conclusion:
The NCS125-2 sensor can measure a 6000A peak on the signal output IS2 with a resistance of 416.67 Ω (greater than 350 Ω) because the output current is smaller than ISMAX i.e. 20mA d.c..The product of RM x ISMAX must always be smaller than or equal to maximum output of 7V d.c..
3 - Measurement circuit calculation (voltage output)
No special calculation needs to be made. This NCS sensor range supplies a voltage directly proportional to the primary current IP between -10V and +10V. A load resistance of a value greater than or equal to 10kΩ adapts the impedance of the measured output (VS1 or VS2) to the acquisition system.