E-Load simulator

The E-Load simulator is a local SCPI server for development, tests, and demos. It listens on a TCP socket, exposes a programmable electronic-load command set, and includes a terminal UI for editing the simulated source and channel limits while your code is running. Each channel sinks current from a simulated Thevenin source: an open-circuit voltage behind a series resistance. The channel regulates in constant current (CC), constant voltage (CV), constant power (CP), or constant resistance (CR) mode. When the source cannot satisfy the setpoint, the channel reports the UNREG state.

Quickstart

Start the simulator in one terminal:

python -m instro.eload.scpi_sim_server

It binds to 127.0.0.1:5026 by default. If you are working from a source checkout, run the same command through uv:

uv run python -m instro.eload.scpi_sim_server

Connect from another terminal or script with the SimulatedELoad driver. This small Python client opens an InstroELoad, configures a 2 A constant-current draw, and reads voltage and current measurements:

from instro.eload import InstroELoad, LoadMode
from instro.eload.drivers import SimulatedELoad


with InstroELoad(
    name="bench_load",
    driver=SimulatedELoad("TCPIP0::127.0.0.1::5026::SOCKET"),
) as eload:
    eload.set_mode(LoadMode.CC, channel=1)
    eload.set_level(2.0, channel=1)
    eload.output_enable(True, channel=1)

    voltage = eload.get_voltage(channel=1)
    current = eload.get_current(channel=1)
    print(f"V: {voltage.latest:.3f} V")
    print(f"I: {current.latest:.3f} A")

    eload.output_enable(False, channel=1)

Use CLI flags to change the bind address, port, or initial channel count:

python -m instro.eload.scpi_sim_server --host 127.0.0.1 --port 5026 --channels 1

Usage

The simulator runs a terminal UI while the TCP server listens in the background. The UI is organized by panel header.

Filled labels are selectable actions. Use the arrow keys to move between controls. Focused actions use a light highlight. Press Enter to select an action, Escape to close an edit prompt, and q to quit.

E-Load

The ⟢ NOMINAL E-LOAD panel shows the simulator identity and VISA resource string. Use the resource string when driver code connects to the simulator.

Channel

Each CHANNEL panel shows the live state for one input. The panel is split into status, setpoint, and measurement sections.

Header	Functionality
STATUS	Shows the operating state (`OFF`, `CC`, `CV`, `CP`, `CR`, `UNREG`, `SHORT`), active function, input state, short state, and CV current limit. Select REMOVE to delete the channel from the simulator.
SETPOINTS	Shows the CC, CV, CP, and CR setpoints and the active function’s range. Select I MAX to edit the channel current ceiling.
MEASURE	Shows terminal voltage, input current, input power, and the rise and fall slew rates. Select V MAX to edit the channel voltage ceiling.

Changing I MAX or V MAX runs *RST. The input turns off, setpoints return to zero, and ranges and the CV current limit return to the configured ceilings.

Source

The SOURCE panel shows the simulated Thevenin source feeding the channel. Select V to edit the open-circuit voltage in volts. Select R to edit the series resistance in ohms.

+ channel

The + CHANNEL panel adds a new input channel with the next available channel ID.

SCPI log

The SCPI LOG panel records incoming commands, responses, and queued errors. It is read-only.

Programming guide

Brackets mark optional SCPI path components. For example, [SOURce:]CURRent[:LEVel] accepts CURR, CURR:LEV, SOUR:CURR, and SOUR:CURR:LEV. Angle brackets mark command arguments. They are notation only; do not include the angle brackets in the command.

<NRf+> is a positive flexible numeric value, such as 0, 1.25, or 1e-3.
<literal|literal> is one literal value from the listed options.

The pipe character (|) means OR. For example, <0|1|OFF|ON> accepts 0, 1, OFF, or ON, and <NRf+|MIN|MAX> accepts one numeric value, MIN, or MAX. Do not send the pipe character in the command. For level commands, MIN maps to 0 and MAX maps to the active range for that function. For range and current-limit commands, MAX maps to the channel ceiling (I MAX, V MAX, and the fixed power and resistance ceilings). For slew commands, MIN and MAX map to the slew-rate bounds. Do not send MIN or MAX to queries. Setting a range below the current setpoint clamps the setpoint down to the new range.

Defaults and reset

On startup and after *RST, each channel uses the reset operating state:

Setting	Reset value
Function	`CURR` (CC)
CC, CV, CP, CR setpoints	`0`
Ranges	`MAX`
CV current limit	`MAX`
Slew rise and fall	`MAX`
Input state	`OFF`
Short state	`OFF`

*RST preserves simulator configuration, including channel count, channel IDs, source voltage, source resistance, and configured channel ceilings.

Error queue

Errors are queued and returned one at a time by SYSTem:ERRor?. The simulator can emit these error codes:

Code	Message	Cause
`0`	`No error`	The queue is empty
`-108`	`Parameter not allowed`	A query received an argument
`-109`	`Missing parameter`	A command was sent without a required argument
`-113`	`Undefined header`	The command header is not supported
`-114`	`Header suffix out of range`	The command targets a channel that does not exist
`-141`	`Invalid character data`	A numeric argument could not be parsed
`-222`	`Data out of range`	A numeric input is outside its accepted range
`-224`	`Illegal parameter value`	A literal argument is not accepted for that command

Common commands

`*IDN?`
Query simulator identity	Response: String
`*RST`
Reset channel operating state and clear errors	Response: None
`*CLS`
Clear the error queue	Response: None

MEASure subsystem

`MEASure:CURRent?`
Measure input current	Response: Number
`MEASure:VOLTage?`
Measure terminal voltage	Response: Number
`MEASure:POWer?`
Measure input power	Response: Number

With the input off, MEASure:VOLTage? returns the source open-circuit voltage and MEASure:CURRent? returns 0.

INPut subsystem

`INPut[:STATe] <0\|1\|OFF\|ON>`
Enable or disable the input	Response: None
`INPut[:STATe]?`
Query input state	Response: `0` or `1`
`INPut:SHORt[:STATe] <0\|1\|OFF\|ON>`
Apply or release the input short	Response: None
`INPut:SHORt[:STATe]?`
Query short state	Response: `0` or `1`

SOURce subsystem

`[SOURce:]FUNCtion <CURRent\|VOLTage\|POWer\|RESistance>`
Select the regulation function (CC, CV, CP, CR)	Response: None
`[SOURce:]FUNCtion?`
Query the regulation function	Response: `CURR`, `VOLT`, `POW`, or `RES`
`[SOURce:]CURRent[:LEVel][:IMMediate] <NRf+\|MIN\|MAX>`
Set the CC setpoint (amperes)	Response: None
`[SOURce:]CURRent[:LEVel][:IMMediate]?`
Query the CC setpoint	Response: Number
`[SOURce:]VOLTage[:LEVel][:IMMediate] <NRf+\|MIN\|MAX>`
Set the CV setpoint (volts)	Response: None
`[SOURce:]VOLTage[:LEVel][:IMMediate]?`
Query the CV setpoint	Response: Number
`[SOURce:]POWer[:LEVel][:IMMediate] <NRf+\|MIN\|MAX>`
Set the CP setpoint (watts)	Response: None
`[SOURce:]POWer[:LEVel][:IMMediate]?`
Query the CP setpoint	Response: Number
`[SOURce:]RESistance[:LEVel][:IMMediate] <NRf+\|MIN\|MAX>`
Set the CR setpoint (ohms)	Response: None
`[SOURce:]RESistance[:LEVel][:IMMediate]?`
Query the CR setpoint	Response: Number
`[SOURce:]CURRent:RANGe <NRf+\|MIN\|MAX>`
Set the CC range (amperes)	Response: None
`[SOURce:]CURRent:RANGe?`
Query the CC range	Response: Number
`[SOURce:]VOLTage:RANGe <NRf+\|MIN\|MAX>`
Set the CV range (volts)	Response: None
`[SOURce:]VOLTage:RANGe?`
Query the CV range	Response: Number
`[SOURce:]POWer:RANGe <NRf+\|MIN\|MAX>`
Set the CP range (watts)	Response: None
`[SOURce:]POWer:RANGe?`
Query the CP range	Response: Number
`[SOURce:]RESistance:RANGe <NRf+\|MIN\|MAX>`
Set the CR range (ohms)	Response: None
`[SOURce:]RESistance:RANGe?`
Query the CR range	Response: Number
`[SOURce:]CURRent:LIMit <NRf+\|MIN\|MAX>`
Set the CV-mode current limit (amperes)	Response: None
`[SOURce:]CURRent:LIMit?`
Query the CV-mode current limit	Response: Number
`[SOURce:]CURRent:SLEW[:BOTH] <NRf+\|MIN\|MAX>`
Set the rise and fall slew rates together (A/μs)	Response: None
`[SOURce:]CURRent:SLEW:RISE <NRf+\|MIN\|MAX>`
Set the rising-edge slew rate (A/μs)	Response: None
`[SOURce:]CURRent:SLEW:RISE?`
Query the rising-edge slew rate	Response: Number
`[SOURce:]CURRent:SLEW:FALL <NRf+\|MIN\|MAX>`
Set the falling-edge slew rate (A/μs)	Response: None
`[SOURce:]CURRent:SLEW:FALL?`
Query the falling-edge slew rate	Response: Number

SYSTem subsystem

`SYSTem:ERRor?`
Pop one error from the error queue	Response: `code,“message”`

Getting started

Concepts

Instruments

Protocols

Transports

Migration

E-Load simulator

E-Load simulator

Quickstart

Usage

E-Load

Channel

Source

+ channel

SCPI log

Programming guide

Defaults and reset

Error queue

Common commands

MEASure subsystem

INPut subsystem

SOURce subsystem

SYSTem subsystem

​E-Load simulator

​Quickstart

​Usage

​E-Load

​Channel

​Source

​+ channel

​SCPI log

​Programming guide

​Defaults and reset

​Error queue

​Common commands

​MEASure subsystem

​INPut subsystem

​SOURce subsystem

​SYSTem subsystem

E-Load simulator

Quickstart

Usage

E-Load

Channel

Source

+ channel

SCPI log

Programming guide

Defaults and reset

Error queue

Common commands

MEASure subsystem

INPut subsystem

SOURce subsystem

SYSTem subsystem