Technical Info: Understanding Current Measurement – Advantages of the PSA Series
Basic Principles of Current Measurement
When current flows through a resistor, a voltage is generated across it according to Ohm's Law.
By measuring this voltage, the current value can be calculated.
The resistor used for current measurement is called a shunt resistor.
Ohm's law
V
=
I
x
R
↓
↓
↓
Volltage [V]
Current [A]
Resistor [Ω]
Current→→→→→→→
Current sensing shunt resistor R
Input
Load
Voltage is generated at both ends of the resistor
This voltage is measured and converted to current
Low-Side Measurement vs. High-Side Measurement
The measurement method varies depending on where the current measuring instrument is installed.
Low-Side Measurement
The instrument is installed between the load circuit and GND (0V).
■ Since the instrument sits between GND and the load, the circuit becomes floating from GND.
■ If a short circuit occurs between the power supply and GND (due to circuit failure, etc.), the short may go undetected as current does not flow through the instrument.
High-Side Measurement
The instrument is installed between the power supply and the load circuit.
■ The load circuit reference remains at GND, but the instrument floats, making it more susceptible to noise.
■ Short circuits between the power supply and GND can be detected and used to trigger alarms.
The PSA series supports both low-side and high-side measurement.
About Shunt Resistors: Part 1 (Voltage Drop)
When current flows through a shunt resistor, the resistor itself consumes power.
To accurately measure high currents or low-voltage devices (e.g., smartphones/wearables at 3.3V or 1.2V), it is essential to use low-resistance shunts or high-power compatible components.
Example 1: When 1A flows from a 3.3V supply with a 1Ω shunt resistor...
Supply voltage to the target circuit
= Source voltage (3.3V) - Shunt resistor voltage drop (1V)
= 2.3V
The supply voltage drops to 2.3V, which may prevent the target circuit from operating correctly.
Therefore, a low-resistance shunt is required.
If a 0.04Ω shunt resistor is used:
3.3V - (1A x 0.04Ω) = 3.26V
The loss is minimized, ensuring stable operation
About Shunt Resistors: Part 2 (Power Loss)
Another critical parameter in current measurement is power loss.
Using the same example (3.3V supply, 1A current), let's calculate the power loss for a 1Ω shunt.
Power (W) = I (Current) x I (Current) x R (Resistance)
Example 2: Power loss with a 1Ω shunt resistor at 1A...
Power loss of the shunt resistor (W)
= 1A x 1A x 1Ω
= 1W
Power loss equals heat generation.
Since electronic components like resistors change their characteristics due to heat, high power loss directly leads to measurement errors.
If a 0.04Ω shunt resistor is used:
W = 1A x 1A x 0.04Ω = 0.04W
Minimal loss and significantly reduced heat generation
Introduction to the PSA Series DC Ammeters (Signal Converters)
The COCORESEARCH PSA series utilizes exceptionally low input (shunt) resistance compared to competitors to minimize voltage drop and power loss.
It features high 16-bit resolution for both input and output.
Advantages of Low Shunt Resistance
■ Comparison: ±2A Measurement Range Models
Company
COCORESEARCH
Competitor Reference
Model
PSA-2401U2D3
------
Range
±2000.0mA
±1999.9mA
Shunt Resistance
Approx. 40mΩ
Approx. 100mΩ
Input Overload
±3A
±3A
Voltage Drop Comparison
Power Loss Comparison
■ Comparison: ±20mA Measurement Range Models
Company
COCORESEARCH
Competitor Reference
Model
PSA-2401U2D1
------
Range
±20.000mA
±20mA
Shunt Resistance
Approx. 1Ω
Approx. 10Ω
Input Overload
±3A
±50mA
Voltage Drop Comparison
Power Loss Comparison
16-bit Input/Output Resolution
Input resolution determines how finely an measured analog signal can be converted into digital data, which is a crucial parameter for precision.
The PSA series features 16-bit resolution for both input and output, allowing for detailed measurement and control.
16-bit refers to 2 to the 16th power (2^16 = 65,536 counts).
Ex: Comparison of Input Resolution in ±2A Range
Resolution (bit)
Steps
Min. Value
Unit
10
1,024
3.906250
mA
12
4,096
0.976563
13
8,192
0.488281
16
65,536
0.061035
Ex: Comparison of Output Voltage Precision (±10V Range)
Resolution (bit)
Steps
Min. Value
Unit
10
1,024
19.531250
mV
12
4,096
4.882813
13
8,192
2.441406
16
65,536
0.305176
13-bit (8192) vs. 16-bit (65536) 16-bit resolution is 8 times finer than 13-bit.
Summary: COCORESEARCH PSA Series DC Ammeters
■ Low Shunt Resistance
→ Low loss allows measurement across a wide range of voltages.
→ Designed to minimize temperature-related errors caused by self-heating.
→ High-overload resistance prevents common failures.
→ Equipped with proprietary analog noise-reduction technology developed for F/V converters.
* Performance has been verified and evaluated by major automotive manufacturers.
■ 16-bit High Resolution
→ Enables ultra-detailed measurement and output.
→ Advanced analog technology ensures precision by effectively eliminating signal noise.
DC Current Input (Ammeters, Signal Converters, Distributors)
Key Features
- Ideal for real-time PWM current measurement and feedback control.
- Shunt resistance ≦ 40mΩ ensures low loss, perfect for charging current evaluation [±10A, ±5A, ±2A models].
- 13 models covering measurement ranges from ±100μA to ±10A.
- Versatile Outputs: CAN, 16-bit Analog, Alarms, RS-485, Modbus, USB, and more.
- Free software for configuration management, report printing, and data logging.
■ Simultaneous 16-bit Analog and CAN output: 1ms update
■ Configuration and logging via USB.
■ PSA-2401: With display, Panel mount type.
■ PSA-2451: Without display, DIN rail mount type.
■ PSA-2431: With display, DIN rail mount type.
■ Simultaneous 16-bit Analog and CAN output: 40ms update
■ Configuration and logging via USB.
■ PSAL-2401: With display, Panel mount type.
■ PSAL-2451: Without display, DIN rail mount type.
■ PSAL-2431: With display, DIN rail mount type.
- CAN and 16-bit Analog (V/I) Output
- USB-C: Configuration and Data Logging
- Alarm Output / RS-485
- Free software: Settings, Reporting, and Logging
EX48: From 35,800 JPY
EX(L)24: From 14,100 JPY
Customized Products (Proven Track Record – Available from Single Units)
We receive many requests for customization, such as "Multi-channel measurement in one unit" or "Specific housing requirements."
COCORESEARCH supports custom orders starting from one unit. Please feel free to contact us.
