  # FMCC EUROPE Components and technical solutions for power electronics Calculation guide
Electronic technology voltage sensors
VS sensors

1 - Reminder of the key elements

 Formulas: Abbreviations VM = RM x IS and UPN/ISN=UP/IS VS50 ... VS1500:● RM = [(0,8 x VAMIN) / IS] - 55● UHT+ + UHT- ≤ 4.2 kV peak    and | UHT+ - UHT- | ≤ UPMAXVS2000 ... VS4200 :● RM = [(0,8 x VAMIN) / IS] - 60● UHT+ + UHT- ≤ 10 kV peak    and | UHT+ - UHT- | ≤UPMAX UP  : primary voltageUPN : nominal primary voltageIS : secondary currentISN: nominalsecondary current VA : supply voltageVAMIN : VA less lowest supply toleranceVM : measuring voltageRM : measuring resistance

Reminder of the sensor electrical connection 2 - Measurement circuit calculation (secondary part of the sensor)

Example with VS1000B sensor

 UPN = 1000V ISN = 50mA VA = ±24V (±5%) UPMAX = 1500V

2.1 - What load resistance (RM) is required to obtain a 10V measuring signal (VM = 10V) when the voltage UPMAX = 1500V peak?

 IS = ISN x UPMAX / UPN = 0,050 x 1500 / 1000 i.e. IS = 75mA RM = VM / IS = 10 / 0,075 i.e. RM = 133,33Ω

We must check that the sensor can measure this 1500V with a ±24V (±5%) supply

 VAMIN = 24 x 0,95 = 22,8V RM = [(0,8 x VAMIN) /  IS] - 55 = [(0,8 x 22,8) / 0,075] - 55 i.e. RM = 188,2Ω

We therefore verify that the sensor can measure this 1500V voltage since the measuring resistance with a ±24V (±5%) supply is 188.2Ω for 133.33Ω required.

Conclusion :
A VS1000B sensor can measure a peak of 1500V in the following conditions:
VA = ±24V (±5%)
RM = 133,33Ωto obtain a 10V signal at 1500V peak.

2.2 - What are the consequences, if the required signal is only 5V (VM = 5V)?

In the same way as for closed loop Hall effect current sensors (see page 109), if the required measuring voltage is reduced, carefully check that the ±15V (±5%) supply used in this example is sufficient to obtain a 5V signal with the conditions used in the preceding point.

 RM = VM / IS = 5 / 0,075 i.e. RM = 66,67Ω RM = [(0,8 x VAMIN) /  IS] - 55 = [(0,8 x 14,25) / 0,075] - 55 i.e. RM = 97Ω

We therefore verify that the sensor measures this 1500V voltage since the measuring resistance with a ±15V (±5%) supply is 97Ω for 66.67Ω required.

2.3 - What is the maximum measurable voltage by a VS1000B in specific conditions?

An electronic voltage sensor is also sensitive to the thermal aspect.In general, a VS voltage sensor can continuously withstand up to 150% of the nominal primary voltage, but only under certain conditions.In all these cases, we recommend that you contact your distributor in order to obtain detailed information on this subject.

2.4 - What influence does the ambient temperature have on the sensor's performance?

The electronic voltage sensor design means that the maximum operating temperature influences the sensor's performance, notably the measurement accuracy. However there is no correlation between a reduction in the ambient temperature and an increase in the voltage to be measured.

2.5 - What influence does the supply voltage have on the sensor performance?

In general, the higher the supply voltage, the higher the measuring voltage. The thermal aspect of the sensor should be considered.NB: for calculations with unipolar supply (e.g. 0...+24V), contact your distributor.

3 - Sensor primary circuit calculation

Maximum common mode voltage:
Can the VS1000B sensor (UPMAX = 1500V peak) be used to measure a differential voltage UP = UHT+ - UHT- with UHT+ = 3500V d.c. and UHT- = 2600V d.c. ?

3.1 - |UHT+ - UHT- | = | 3500 - 2600 | = 900V d.c. ≤ 1500V peak :
First condition | UHT+ - UHT- | < UPMAX is therefore fulfilled.

3.2 - UHT+ + UHT-  =  3500 + 2600  = 6100V d.c. ≤ 4.2kV peak :
Second condition  UHT+ + UHT-  ≤ 4.2kV peak is not therefore fulfilled.

Conclusion :

The VS1000B sensor cannot therefore be used to measure this 900V d.c. primary differential voltage (even though this differential voltage is lower than the nominal primary voltage of the VS1000B sensor).

For this application the VS2000B sensor can be used since:

UHT+ + UHT-= 6100V d.c. ≤ 10kV peak

The condition UHT+ + UHT- < 10kV peak is therefore fulffilled with the VS2000B.