Just as device gain variants constrain where a device can be placed, the full-scale range set by the user also impacts device placement. The A3 variant was used and four different full-scale range (FSR) values chosen: 300 A, 600 A, 1200 A, and 2000 A. Figure 6-5 shows the error vs bus bar to sensor PCB distance for each of the chosen FSRs. The device spacing was fixed at 9.5 mm which corresponds to the edge of the bus bar; this is the same as the setup in Section 6.1.3.1.

For this setup, the FSR plots reveal that low full-scale ranges (300 A) create a tight window for acceptable PCB distances (roughly 3-4 mm), while high FSR values (2000 A) shift this window farther away but introduce a different constraint—the minimum distance from the bus bar cannot be too close, or saturation error emerges. This creates a design optimization problem: the FSR choice must be compatible with the mechanical mounting distance. If the system requires 2000 A full-scale but the thermal or space constraints force the PCB too close to the bus bar, there could be significant error. In such cases, revise either the FSR (by accepting lower full-scale current measurement), choose a lower device gain variant, or modify the mechanical design (by finding additional PCB clearance).

Figure 6-5 Error vs Distance to PCB (different FSRs)

Figure 6-6 shows the error vs different device spacings when the distance from the bus bar to the sensor PCB is fixed at 4 mm. Device spacing is not a limiting factor at 600 A, 1200 A, and 2000 A FSR. At 300 A FSR, however, placement beyond 11 mm from the bus bar center produces significant errors. This occurs because lower FSR ranges require higher gain to reach full scale (VS), making the device more sensitive to signal attenuation over distance.

Figure 6-6 Error vs Device Spacing (different FSRs)