Basic Principles of Current Measurement

When a current flows through a resistor, a voltage is generated at both ends of the resistor according to Ohm's law.
The voltage applied to both ends of the resistor is measured and converted to a current value. 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/High Side Measurement

The measurement method differs depending on the location of the current measurement device.

Low-side measurement	High-side measurement
Install a current meter between the circuit to be measured and GND (0V).	Install a current meter between the power supply and the circuit to be measured.
- Since the current measurement device is located between the GND and the circuit to be measured, the circuit floats away from the GND. - If the GND and power supply are short-circuited due to a fault in the circuit to be measured, the short-circuit is not detected because no current flows to the current measurement device.	- Although the reference of the circuit to be measured can be set to GND, the measuring instrument floats above the GND and is easily affected by noise. - Even if GND and power supply are short-circuited due to a malfunction in the circuit to be measured, a short-circuit can be detected and an alarm can be issued.

The PSA series supports both high-side and low-side measurements.

About Shunt Resistors Part 1

When current flows through a resistor (shunt resistor) used for current measurement, the resistor itself consumes power.
Low drive voltage products such as smartphones and wearable devices (3.3V / 1.2V, etc.) and high current measurement with high accuracy require support for low resistance and high current.

Example 1: Supply voltage of 3.3V, current of 1A, and shunt resistance of 1Ω

Supply voltage to the circuit to be measured = voltage between power supply voltage and shunt resistor = 3.3V-1V = 2.3V The voltage supplied to the circuit is 2.3V, this makes it difficult to know if the circuit will operate properly. Therefore, a shunt resistor with a low resistance value should be used. If the shunt resistor is 0.04Ω 3.3V-（1A×0.04)=3.26V This is fine because the loss is low!

About Shunt Resistance Part 2

Another important parameter in current measurement is power loss.
Similar to the previous example, let us calculate the power loss for a current of 1A at a power supply of 3.3V and a shunt resistance value of 1Ω.
Power (W) = I (current) x I (current) x R (resistance)

Example 2: Supply voltage of 3.3V, current of 1A, and shunt resistance of 1Ω

Power dissipation of shunt resistor (W) = 1A x 1A x 1Ω ＝1W Power loss = heat generation. Since resistors and other electronic components change their characteristic values due to heat, a large amount of power loss will lead to measurement errors. If the shunt resistance is 0.04Ω, the power loss is W=1A×1A×0.04＝0.04W Less loss and less heat generation!

Introduction of PSA Series of Current Measuring Instruments

COCORESEARCH's PSA series uses smaller input shunt resistors than other companies' products to minimize voltage and power losses.
The input and output resolution is as high as 16 bits.

Advantages of Low Shunt Resistance

- Comparison with ±2A measuring range products

Company name	Type	Measurement range	Shunt Resistance	Input overload
COCORESEARCH	PSA-2401U2D3	±2.0000A	Approx. 40mΩ	±3A
Reference value for other companies	－－－－－－	±1999.9mA	Approx. 100ｍΩ	±3A

Voltage Drop Comparison	Power Dissipation Comparison

- Comparison with ±20mA measurement range products

Company name	Type	Measurement range	Shunt Resistance	Input overload
COCORESEARCH	PSA-2401U2D1	±20.000mA	Approx. 1Ω	±3A
Reference value for other companies	－－－－－－	±20mA	Approx. 10Ω	±50mA

Voltage Drop Comparison	Power Dissipation Comparison

16bit input/output resolution

How finely a measurement value can be measured and output is an important parameter.
When measured analog signals are converted to digital data inside the instrument, the input resolution determines how finely the signals can be digitized.
The PSA series has a resolution of 16 bits for both input and output, enabling detailed measurement and output.
16bit means 16th power of 2. (2^16 = 65535 counts)

Ex: Comparison of input resolution fineness in ±2A range Resolution (bit) Number of data Minimum measurement value Unit 10 2^10 = 1024 3.906250 mA 12 2^12 = 4096 0.976563 13 2^13 = 8192 0.488281 16 2^16 = 65536 0.061035
Ex: Output voltage fineness comparison with ±10V analog output Resolution (bit) Number of data Minimum measurement value Unit 10 2^10 = 1024 19.531250 mV 12 2^12 = 4096 4.882813 13 2^13 = 8192 2.441406 16 2^16 = 65536 0.305176	13bit = 8192  vs 16bit = 65536 16bit can measure 8 times finer than 13bit.

Summary of COCORESEARCH's PSA series DC ammeter

Low shunt resistance

　- Low shunt resistance and low loss, enabling measurement of a wide range of products from low to high voltages.

　- Designed to minimize temperature error due to self-loss.

　- Designed to withstand high load voltage and to resist breakdowns.

　- Equipped with analog technology (noise reduction technology) accumulated in F/V converters.

　　　Operation has been tested and verified by an automobile company.

 

High resolution of 16 bits

　- High resolution of 16bit.

　- Analog technology (noise elimination) accumulated in F/V converters is incorporated to enable detailed and accurate measurement.

Applications

→ Click here for a list of applications

Real-time measurement of PWM drive current of solenoid valves, etc.	Measurement and management of CCCV charging current of lithium-ion battery and charger	Incorporation into burn-in test equipment

Products

Common features of each product
- Suitable for real-time measurement and feedback control of PWM current of solenoid valves (proportional control valves)
- Shunt resistance of 40mΩ or less ensures low loss, making it ideal for charging current evaluation.

Products		Points	Overviews
	PSA-2401	Current measurement	24x48 size DC ammeter. Simultaneous 16-bit analog and CAN outputs with 1 ms updates. LINKSHIP" compatible product that enables power supply/logging/setting via USB.
	PSA-4801	Current measurement	48x96 size DC ammeter. Simultaneous 16-bit analog and CAN output with 1ms update. LINKSHIP" compatible with USB for logging/setting.
	PSAL-2401	Low cost	24x48 size DC current meter. Simultaneous 16-bit analog and CAN outputs with 40ms updates. LINKSHIP" compatible product with USB power supply/logging/setting.