Phoenix Contact SCK-M-U-1500V Handleiding (128 Pagina's)

Handleiding

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105608_en_02 PHOENIX CONTACT 67

8.3 System calibration

The measuring inputs of all measuring modules are tested and calibrated to high quality

standards in the factory. However, due to the physical characteristics of Hall sensor mea-

surement, under certain circumstances, it is possible to generate an offset in the current

measured value that has been caused by magnetization. Very abrupt current edges, which

are rather unusual in photovoltaics, or geological conditions can cause such effects.

Where present, this measured value offset is usually consistent. This means that the mea-

sured values are always increased by the same basic value. This type of offset can be de-

tected permanently when the PV generator is switched off but a constant low current value

is still displayed above the specified deviation of measurement. For example, at night when

it is guaranteed that there is no current flowing and the displayed measured value is, e.g.,

0.4 A.

In this type of situation, the entire measuring system can simply be calibrated.

To do this, the current value of all measuring channels is recorded in a defined “zero-current

situation” (e.g., at midnight) and temporarily stored. This value is the offset by which the ac-

tual current values are increased during daytime operating hours.

Take this temporarily stored value and permanently subtract it from the measured value re-

corded during the day.

This zero calibration can also be performed each night as standard, for example, to improve

general measuring accuracy, without an actual offset having been generated.

Figure 8-2 System calibration

I = 6,7 A

I = 6,3 A

I = 6,1 A

PV 1

PV 2

PV 3

I = 0,4 A

I = 0,2 A

I = 0,0 A

PV 1

PV 2

PV 3

I=

N

0 A

I = 6,7 A (-0,4 A) = 6,3 A

I=

PV 1

PV 2

PV 3

6,3 A (-0,2 A) = 6,1 A

6,1 A (-0 A) = 6,1 A

=

~

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