The miniSMU MS01 offers versatile measurement capabilities through its different operating modes. This section explains how to set and use the two primary measurement modes: Force Voltage, Measure Current (FVMI) and Force Current, Measure Voltage (FIMV).

Understanding Measurement Modes

Before selecting a measurement mode, it's important to understand the differences between them:

Force Voltage, Measure Current (FVMI) Mode

In FVMI mode, the miniSMU MS01 acts as a voltage source:

• The voltage across the device under test is maintained at your set value
• The miniSMU adjusts its output current as needed to maintain this voltage
• The applied voltage and current flowing through the device is measured and reported

When to Use FVMI Mode

FVMI mode is ideal for:

• Resistor characterisation: Apply a known voltage and measure the current to calculate resistance
• Diode testing: Generate I-V curves by sweeping voltage and measuring current
• Solar cell testing: Apply reverse bias voltages and measure leakage currents
• LED characterisation: Control voltage precisely and observe current consumption
• Transistor testing: Apply specific gate-source voltages and measure drain current

To enable FVMI mode on a specific channel, use the SOURx:FVMI ENA command, where x is the channel number (1 or 2):

SOURx:FVMI ENA

Example:

SOUR1:FVMI ENA

This enables FVMI mode on channel 1.

Complete FVMI Configuration Example:

SOUR1:VOLT 3.3        # Set channel 1 to output 3.3V
SOUR1:CURR:PROT 0.02  # Limit current to 20mA for protection
SOUR1:FVMI ENA        # Enable FVMI mode
OUTP1 ON              # Enable the output
MEAS1:CURR?           # Measure the resulting current

Force Current, Measure Voltage (FIMV) Mode

In FIMV mode, the miniSMU MS01 acts as a current source:

• The current through the device under test is maintained at your set value
• The miniSMU adjusts its output voltage as needed to maintain this current
• The voltage across the device and current flowing through the device is measured and reported

When to Use FIMV Mode

FIMV mode is ideal for:

• Battery testing: Apply a specific charging/discharging current and measure voltage response
• Low-resistance measurements: Force a known current and measure the small voltage drop
• Temperature sensor characterisation: Drive constant current through RTDs or thermistors
• LED brightness control: Precisely control LED current for consistent brightness
• Current-driven devices: Test components that require current-based operation

To enable FIMV mode on a specific channel, use the SOURx:FIMV ENA command:

SOURx:FIMV ENA

Example:

SOUR2:FIMV ENA

This enables FIMV mode on channel 2.

Complete FIMV Configuration Example:

SOUR2:CURR 0.01       # Set channel 2 to output 10mA
SOUR2:VOLT:PROT 5     # Limit voltage to 5V for protection
SOUR2:FIMV ENA        # Enable FIMV mode
OUTP2 ON              # Enable the output
MEAS2:VOLT?           # Measure the resulting voltage

Mode-Specific Considerations

FVMI Mode Considerations

• Open Circuit Behavior: In FVMI mode with an open circuit, the measured current will be very close to zero
• Short Circuit Risks: Be especially careful with FVMI mode when there's a risk of short circuit, as current can increase rapidly
• Current Limiting: Always set appropriate current protection limits before enabling output
• Compliance Indication: If the current protection limit is reached, the channel LED will turn red

FIMV Mode Considerations

• Open Circuit Behavior: In FIMV mode with an open circuit, the miniSMU will increase voltage until reaching the protection limit
• Zero-Volt Sources: FIMV mode is excellent for testing devices that operate near zero volts (e.g., supercapacitors, some battery types)
• Voltage Limiting: Always set appropriate voltage protection limits before enabling output
• Compliance Indication: If the voltage protection limit is reached, the channel LED will turn red

4-Wire Kelvin Sensing Mode

4-wire (Kelvin) sensing eliminates lead and contact resistance from your measurements by using separate force and sense connections.

How It Works

In 4-wire mode:

• Channel 1 acts as the force (source) channel
• Channel 2 acts as the sense channel in high-impedance mode
• Voltage is measured at the sense terminals, bypassing any voltage drop in the force leads

When to Use 4-Wire Mode

4-wire mode is ideal for:

• Low-resistance measurements where lead resistance significantly affects accuracy
• High-precision voltage measurements on devices with contact resistance
• Battery internal resistance measurements
• Connector and contact resistance testing

Enabling 4-Wire Mode

Via miniSMU App (v1.1.0+): Navigate to Settings > About and enable the 4-Wire Mode toggle (only visible when connected).

Via Python Library (v0.3.0+):

smu.enable_fourwire_mode()   # Enable 4-wire mode
smu.disable_fourwire_mode()  # Disable 4-wire mode
status = smu.get_fourwire_mode()  # Query current state

Via SCPI Commands:

SYST:4WIR ENA    # Enable 4-wire mode
SYST:4WIR DIS    # Disable 4-wire mode
SYST:4WIR?       # Query 4-wire mode status

Important Notes

• When 4-wire mode is active, Channel 2 cannot be used independently
• OUTP1 ON/OFF controls both channels together in 4-wire mode
• 4-wire mode cannot be enabled while streaming or sweep is active
• In the miniSMU app, Channel 2 controls are disabled with a tooltip explaining why