calibration

RocketLogger Calibration

Requirements

• The RocketLogger to calibrate, with initial hardware tests passed and software installed
• A Keithley 2450 SMU
• Two SMU probe cables
• RocketLogger test leads
• A 1k resistor for the low current measurements
• An USB power bank (5V) with 1A+ current rating to decouple SMU and RocketLogger to calibrate

Process

It is recommended to read through the full procedure and to have a look a the hints below before starting with the measurements.

Calibration Measurements

1. Power up the RocketLogger. Use the USB power bank to avoid coupling of the SMU with the RocketLogger through the power line...
2. Open your browser and open the RocketLogger's web interface. Use the login you have set during Software Installation.
3. Select the 'Calibration Measurement' option in the web interface.
4. Deselect all analog and digital channels and only enable the ones required for the specific measurement.
5. Capture the following sweeps with the RocketLogger: a) Voltages (V1-V4 in parallel), b) Current Low I1, c) Current Low I2, d) Current High (I1+I2 in series)
   • Configure the RocketLogger web interface and Keithley 2450 SMU as shown in the table below.
   • Set/Change the SMU settings in the order of the table. The voltage measurement settings are also applied for the current measurements if not defined otherwise.
6. Connect the channel to measure to the SMU output (Force)
   • For Voltage Calibration connect all voltage probes in parallel, plus the black wire of one of the current channels (ground).
   • For Current Low Calibration each channel should be calibrated individualy. Connect a 1k resistor in series to the channel being calibrated, disconnect the other current channel's probe.
   • For Current High Calibration both channels in series without shunt resistor. Each of the red wires goes to one of the SMU's terminals, the polority does not matter (automatically detected by calibration script).
7. Run the calibration measurement by
   • Turn on the SMU output
   • Start the measurement on the RocketLogger
   • Press the TRIGGER button on the SMU to run the configured sweep sequence
   • The SMU output is automatically being disable when complete, you can then stop the RocketLogger measurement
   • Move on with the next calibration measurement until you recorded all four traces

Setting	Voltage Calibration	Current Low Calibration	Current High Calibration
RocketLogger Web Interface
Filename	YYYYMMDD_calibration_v.rld	YYYYMMDD_calibration_i{1,2}l.rld	YYYYMMDD_calibration_ih.rld
Sample Rate	1 kSPS	1 kSPS	1 kSPS
Calibration Measurement	ON (check)	ON (check)	ON (check)
Analog Channels Enabled	V1, V2, V3, and V4	either I1L or I2L	I1H and I2H
Force High Range	not relevant	both OFF (uncheck)	both ON (check)
Digital Input Channels	OFF (uncheck)	OFF (uncheck)	OFF (uncheck)
Keithley 2450 SMU Settings
Basic Settings (Menu > Source > QuickSet)
Function (Measurement Mode)	Source Voltage - Measure Voltage	Source Current - Measure Voltage	Source Current - Measure Voltage
Sweep Settings (Menu > Source > Sweep)
Type	Linear Dual	Linear Dual	Linear Dual
Start	-5.0 V	-1.0 mA	-100 mA (1A range not so great)
Stop	+5.0 V	+1.0 mA	+100 mA
Definition	Number of Points	Number of Points	Number of Points
Points	101	101	101
Source Delay	250 ms	250 ms	250 ms
Source Limit	105 uA	2 V	2 V
Source Ranging	Auto	Auto	Auto
Generate	Press Generate to store sweep	Press Generate to store sweep	Press Generate to store sweep
Measure Settings (Menu > Measure > Settings)
Measurement Connection	2-wire	2-wire	2-wire
Voltage Range	Auto	2 V	2 V
Measurement View (Home Button)
Current Range	-	Auto	Auto

Generate Calibration Data File

Download the four measured sweep measurements and run the calibration script in Matlab (see rl_do_cal.m Matlab script)

1. Set the correct filename_prefix in rl_do_cal.m
2. rl_do_cal(0) (set create_plots to 1 to plot the residuals and pareto optimal error figures) generates the calibration file from the measurements
3. Copy calibration.dat to /etc/rocketlogger on the BeagleBone (copy it first to the rocketlogger home /home/rocketlogger)

The Matlab calibration functions and the calibration file format is documented in the Wiki: RocketLogger Matlab Scripts and Calibration File Format.

Hints

• Before triggering the sweep, SMU output has to be on (to avoid noise on the measurement). There should also be a step between the initial measurement and the first calibration level -> set the SMU output to 0 before triggering.
  • Alternatively you can start a sweep and then push the ON/OFF button twice to stop at another level.
• The Matlab script tries to detect the peaks caused by the SMU's internal range switching, they should not cause any problems.