1、 Range and maximum measurement capability, power consumption, supply voltage
The range of the sensor refers to the rated measurement current, and the specific value can be found in the instruction manual of the corresponding model. Under the condition that the load resistance value and supply voltage meet the requirements, the sensor can have full range measurement capability under any normal operating temperature and other conditions. Overload capacity refers to the measurement capability that a sensor can achieve within a limited time range. The maximum measurement capability of a sensor refers to the absolute maximum capacity that can be achieved under ideal conditions. The maximum measurement capability may be limited by the capacity of the internal power transistor and can only be used for a short period of time. Extremely short pulse current measurement, not limited by maximum measurement capability.
The maximum measurement capability of the sensor is shown in Formula 1 below
Among them, IPmax is the maximum measurable current on the primary side (peak value of DC or AC current), KN is the ratio of primary side to secondary side current, VCC is the power supply voltage, V0 is the internally reserved voltage, generally taken as 3V.
RL is the load resistance, and Ri is the internal resistance of the internal coil.
From formula 1, it can be seen that under a fixed KN, the maximum measurable current is positively correlated with the power supply voltage VCC and negatively correlated with the resistors RL and Ri.
The internal resistance Ri of the coil is affected by temperature, as shown in the following formula:
Formula 2 Ri=Ri0 [1+(T-25) α]
Among them, Ri0 is the internal resistance of the coil at 25 ℃, T is the coil temperature, α is the temperature coefficient of copper, and α=0.004.
As the temperature rises, the internal resistance of the coil will increase, resulting in a decrease in maximum measurement capability.
The current consumed by the sensor during operation is:
Formula 3: IS=ISO+IP/KN
Among them, ISO is the current consumed by the sensor when the primary current IP=0.
The total power consumption of the sensing circuit (including the power consumption of the sensor and load resistance)
Formula 4: P=VccIS
The power consumption inside the sensor is mainly due to the consumption of internal coils and power tubes. The consumption of power tubes generates heat, leading to temperature rise. In extreme cases, it may cause overheating of power tubes, resulting in reduced lifespan or even overheating damage.
To avoid energy waste, efficiency decline, and increased burden on power tubes, the lowest power supply voltage that meets the maximum measurement capability should be taken as much as possible, especially when sensors operate in high-temperature environments. The value of the power supply voltage provided in the manual can meet the given range. If the maximum measured value is significantly lower than the range, the power supply voltage can be appropriately reduced. For example, for sensors powered by 15V, the minimum operating voltage is 10V, and it is recommended to use 12V or above. Sensors powered by 18-24V have a minimum operating voltage of 18V, please do not further decrease it.
If it is necessary to increase the measurement capability of the sensor, the power supply voltage can be slightly increased. For example, a sensor powered by 15V can be raised to a maximum of 18V. However, it should be noted that the power consumption on the power tube needs to be strictly controlled at this time.
2、 Excessive travel protection and self recovery function
Magnetic modulation sensors are different from traditional Hall current sensors, which can reach and maintain a magnetic saturation state, that is, stay at the maximum output position, even when the maximum measurement capability is exceeded. Magnetic modulation sensors can only operate in a zero flux state, and cannot stop at the maximum output position when they exceed their maximum measurement capability, that is, when they are in a non-zero flux state. At this point, triggering the internal self recovery function causes the output to enter a scanning state, and the output is completely independent of the input. At this point, the Valid indicator light goes out. Once the primary current returns to the range, the self recovery function will immediately put the sensor into normal working condition (usually in the hundreds of milliseconds).
To avoid the above situation, the load resistor RL can be connected in parallel with two reverse series Zener diodes or bidirectional TVS tubes. When the voltage on RL reaches the reverse conduction voltage of the diode, the diode conducts and splits, equivalent to a variable resistor. At this time, the output voltage of the sensor can remain at the maximum output voltage position.
The above approach has limitations, that is, the total resistance of RL parallel diodes cannot be as low as 0. If it exceeds the maximum measurement capability determined by formula 1, the internal system will still enter a scanning state. Please try to avoid this state as much as possible. If it cannot be avoided, the measurement should be interrupted in this state.
Except for excessive range, factors such as unsynchronized power supply of positive and negative power sources, and power failure of a single power source may trigger the self recovery function.
3、 Accuracy considerations
The output accuracy of the sensor is related to the load resistance RL, especially in measuring AC situations. Generally speaking, the smaller the RL value, the higher the measurement accuracy. Generally, the voltage on RL should not exceed 3V.
Please position the current bus as close as possible to the center of the measuring aperture to improve accuracy. Although the accuracy decrease caused by deviation from the center is much lower than that of Hall current sensors, there is still a certain degree of decrease.
The output accuracy of sensors is affected by temperature, but for magnetic current sensors, the effect of temperature is minimal. The accuracy indicated in the manual is for the entire temperature range.
4、 Frequency characteristics
This type of sensor can obtain high-precision measurement results within 2KHz. As the frequency continues to increase, the rate of accuracy decline accelerates, and at the same time, the maximum measurement capability will also decrease. If measuring high-frequency AC current, attention should be paid to the frequency derating characteristics of the sensor range.
Magnetic modulation sensors will have a certain ripple at the modulation frequency, usually around 2-20uArms, which will have a certain impact on the measurement accuracy of small current input signals.
