And the calibration procedure ,
6. LCR meter calibration
There are 7 calibration menus, totally 10 (15?) parameters to be calibrated, respectively M0~M8 and “M3.”, “M5.”, “M6.”, “M7.” And “M8.”.
M0 is nulling offset at 100Hz, unit is LSB, default to 20.
M1 is nulling offset at 1kHz, unit is LSB, default to 20.
M2 is nulling offset at 7.8kHz, unit is LSB, default to 14.
M3 is phase compensator for VI converter at 20Ohm range, unit is 0.001rad, default to 0.
M4 is phase compensator for VI converter at 1kOhm range, unit is 0.001rad, default to 0.
M5 is phase compensator for VI converter at 10kOhm range, unit is 0.001rad, default to 0.
M6 is phase compensator for VI converter at 100kOhm range, unit is 0.001rad, default to 20.
M7 is second stage PGA phase compensation, unit is 0.001rad, default to 16.
M8 is first stage PGA phase compensation, unit is 0.001rad, default to 20.
“M3.” is lower arm calibration for VI converter at 20Ohms, unit is 1%, default to 0.
“M4.” is lower arm calibration for VI converter at 1kOhms, unit is 1%, default to 0.
“M5.” is lower arm calibration for VI converter at 10kOhms, unit is 1%, default to 0.
“M6.” is lower arm calibration for VI converter at 100kOhms, unit is 1%, default to 0.
“M7.” is second PGA gain calibration, unit is 1%, default to 0.
“M8.” is first PGA gain calibration, unit is 1%, default to 0.
In LCD1602 version, these parameters are called Z0, Z1, Z2, R1X, R2X, R3X, R4X, G1X, G2X, R1, R2, R3, R4, G1 and G2.
To restore factory settings, press C key 5 times to restore default setup, then press L key to save.
Before calibration, a few resistors need to be prepared:
20R, 1k, 10k and 100k resistors are needed for calibration of VI converter.
3.3k and 10k resistors are needed for calibration of PGA (translator’s note: you also need 330R and 100R).
At 1kHz and 7.8kHz, connect 20R, 1k, 10k and 100k resistors when calibrating respective ranges, gain setup of upper and lower arms must be identical in order to calibrate amplitude and phase. Press M+R key to enter checking menu, if “1, 1” is displayed, then both arms are balanced and gains are identical. If display is “0, 1” or “1, 0”, then signal amplitude is incorrect.
Nulling offset calibration (M0, M1, M2)
Ensuring zero nulling offset is the fundamental of precision measurement, and hence it is recommended to be the first step in calibration. Using specified BOM, nulling offset points are also identical across individual builds, hence preset values can be used. In case a calibration is needed, do the following (note: translator added this sentence):
For M0 at 100Hz:
1、Set f=100Hz, range=100k
2、Connect 1% 10R resistor as DUT
3、Read R value from menu 1
At 10k range (100k?), measuring 10R resistor will incur more error and this is normal. If error is above 2%, you need to adjust M0 in order to bring it to within 2%.
M1 and M2 can be calibrated using the same method, at different frequency (1kHz and 7.8kHz).
Buzzer will beep whenever a key is presses, causing higher IO current through MCU and incurring error. Please read values after buzzer stopped beeping.
Phase compensation for VI converter and PGAs (M3~M8)
Set f=7.8kHz, range=1k
1、Connect 20R resistor as DUT, measure Q at 20R range, record Q. Subtract Q with Q0, set M3 to this value (note: Q0 should be Q reading with open circuit DUT. Multiply this number by 1000).
2、Connect 1k resistor as DUT, measure Q at 1k range, record Q. Subtract Q with Q0, set M4 to this value.
3、Connect 10k resistor as DUT, measure Q at 10k range, record Q. Subtract Q with Q0, set M5 to this value.
4、Connect 10k resistor as DUT, measure Q at 100k range, record Q. Subtract Q with Q0, set M6 to this value.
5、Connect 330R resistor as DUT, measure Q at 1k range, record Q. Subtract Q with Q0, set M7 to this value. This calibrates PGA gain=3x mode.
6、Connect 100R resistor as DUT, measure Q at 1k range, record Q. Subtract Q with Q0, set M8 to this value. This calibrates PGA gain=9x mode.
For example, in order to obtain M8, measure a 100R resistor, record Q. For instance, Q=0.020, then set M8=20.
Note: at 1kHz, 1k range, when DUT is between 640R~1k, it is (1, 1) (note: WTF? I can’t understand what he means), when R=440R~640R, it is in hysteresis region. When R=280R~440R, it is (0, 1), when R=250R~280R, it is in hysteresis region. When R=85R~250R, it is (0, 2), then R=75R~85R it is in hysteresis mode, when R<75, it is (0, 3).
Amplitude calibration for VI converter and PGAs (M3 dot to M8 dot)
Multiply error values by 10000.
In respective ranges, at 1kHz, connect 20R, 1k, 10k and 100k resistors, measure error, then save calibration values to M3 dot to M8 dot correspondingly.
The process is similar as the one described before.