When designing metering products with Ruineng micro metering chips, the majority of electronic hardware engineers often 

encounter the situation of selecting different sampling resistors for different current specifications. In view of these requirements, 

the following calculation methods are specially arranged to facilitate the calculation of required values according to the needs.
The following calculation is only applicable to the products with the transformer as the sampling device, and the manganese 

copper sampling is introduced separately.
The determination of sampling resistance must follow two conditions at the same time:
Condition 1: R sampling ≤ transformer load impedance
Condition 2: the selection of R sampling must ensure that the sampling signal does not exceed the full scale V full scale under the 

condition of 1.5 times IMAX
Namely:

V full range: sampling signal limit, current loop transformer secondary sampling voltage range limit. This range has different limit 

requirements for different chips. The details are as follows:

1.5: constant, reserved margin
IMAX: maximum current of the product
K transformation ratio: transformer (CT) transformation ratio
R sampling: secondary series connection resistance of transformer, as shown in the figure below, R sampling = R1 + R2 (R1 = R2)

Gain multiple: the channel current gain multiple in the system control register syscon (0x00), 16 times by default for pgaia [1:0] of 

channel A and 4 times by default for pgaib [1:0] of channel B
Examples:
A new single-phase metering product is designed. The rn8209c \ D \ g metering chip of Ruineng micro is selected. The 5 (60) a / 2.5mA 

transformer is used, the transformation ratio is 2000:1, and the load impedance of the transformer is 10 Ω. The sampling design is pgaia 

[1:0] of channel a, and the gain is 16 times by default. Then the resistance values of the sampling resistors R1 and R2 are calculated as 

follows:

The sampling resistance value satisfying both conditions is 0.982 Ω, that is, R1 and R2 resistance value are 0.982 ÷ 2 ＜ 0.491
Check the resistance value specification table,

Finally determine the precision resistance of R1 = R2 = 0.47 Ω (0r47)