Cirrus Logic CRD5490 - Manual (Page 16)

CRD5490-Z
16 DS988RD1
3.3.5.1 AC Offset / Gain Register
In the AC Offset and Gain fields, the AC offset and gain registers for all channels are displayed in hexadecimal
format. These registers can be modified directly by typing values in the fields and then pressing Enter on the
keyboard. The AC offset register only affects the current channel's I
RMS
register values.
3.3.5.2 Performing Calibrations
To ensure accurate results, Gain calibration should be performed before AC offset calibration. The gain calibration
can be performed on both the voltage and current channels of the CS5490. The AC offset calibration can be
performed only on the current channel. In the CS5490, the initial values in the calibration registers affect the results
of the calibration. The register values are shown in blue in Figure 14. Before calibration, the gain and offset registers
should be configured in their default state 0x 40 0000 (gain = 1) for gain registers and 0x 00 0000 (clear = 0) for
offset registers.
Gain Calibration
For gain calibration, the CRD5490-Z software configures the gain registers prior to setting up calibration based on
the reference meter readings. The CRD5490-Z software uses the non-full scale gain calibration techniques and
formulas in Appendix 3: Non-Full Scale Gain Calibration (see page 33) to set up the CS5490 voltage and current
channel gain registers before calibration. The AC offset register values are not modified by the software, and the
current configuration are used. The default AC offset register value should be 0x 00 0000.
1. Attach an AC reference meter as configured in Figure 16. It is important to use short and large gauge wires to
attach the reference power meter to reduce error.
2. Attach and turn on an AC source.
3. Attach and turn on AC load. For this example, a 200W light bulb is used, but it is recommended to use a load
that is at a minimum of ½ of the full-scale load current.
CRD5490-Z
AC
SOURCE
AC
Load
GUI
USB
Reference
Power
Meter
(V, A) *
Figure 16. Gain Calibration Configuration