A shunt is a measuring element that uses voltage to indicate current. It is made according to the principle of generating voltage at both ends of the resistor when DC current passes through the resistor. It is connected in parallel with the current circuit of measuring instruments to expand its measurement range; or An element on which voltage is measured, thereby indirectly measuring current.

I. Types

1. Standard shunt

Standard shunts are used to measure direct current and are made according to the principle that a voltage is generated across the resistor when the direct current passes through the resistor.

Shunts are widely used to expand the measuring current range of the instrument. There are fixed fixed-value shunts and precision alloy resistors. They can be used in communication systems, electronic complete machines, automatic control power supplies, and other circuits for current limiting, current sharing, and sampling detection. There are many different specifications of ammeters, but the actual meter head is a standard millivolt voltmeter. For example, a voltmeter with a full scale of 75 millivolts. Then use this voltmeter to measure a current of, say, 20 amperes, and you need to equip it with a shunt resistor that produces a voltage drop of 75 millivolts when a current of 20 amperes flows, also called a 75 millivolt shunt.

2. Network shunt

A network shunt is something similar to a router, or more precisely, it is a crossed network cable. Generally, the network shunt has only a few poor holes, which is not as big as an adult’s fist. One side is plugged in the network cable, and the other is connected to the computer network cable. It is usually a rectangular box with three to four ports outside. When you want to use it, use the network cable directly. Just plug it in.

3. Hydraulic shunt

The pressure divider uses a flexible and efficient way to combine multiple hydraulic pumps and apply them in a multi-circuit hydraulic system. Each shunt includes a series of gear pairs, which divide the input oil into several outputs into equal or proportionate amounts. The working pressure of each path can be different from each other, and each path can be equipped with a safety relief valve.

4. Wire shunt

Wire shunts have now become the first choice for electrical designers of various design institutes. This is mainly because the product is a national patent product. The conductor material used in the product is tinned copper after molding, ensuring that the material selected for the product is the same material as the cable conductor, The connection of the conductor is surface contact, and the protection level of the product reaches IP63.

Wire shunt products cover a wide range of specifications and models, which can fully meet the power distribution methods under various conditions.

II. Working Principle

A shunt is used to measure direct current and is made according to the principle that a voltage is generated across the resistor when the direct current passes through the resistor.

Shunt uses the input data of the network shunt to copy, aggregate, and filter, and converts 10 Gigabit POS data into Gigabit LAN data through protocol conversion, and performs load balancing output according to a specific algorithm, and guarantees all data of the same session while outputting Packets, or all data packets of the same IP user are output from the same interface.

- A shunt is actually a resistor with a small resistance value. When a DC current passes through, it will produce a voltage drop for the DC ammeter to display;

- The DC ammeter is actually a voltmeter, with a full-scale value of 75mV;

- DC ammeter and shunt are used together;

- For example, the resistance value of the shunt matched with a 100A ammeter is 0.00075 ohms, which is 100A*0.00075 ohm=75mV;

- The resistance value of the shunt matched with the 50A ammeter is 0.0015 ohms; 50A*0.0015 ohm=75mV.

To measure a large DC current, such as tens of amperes, or even more, hundreds of amperes, there is no such a large range of ammeters for current measurement, what should I do? This requires the use of shunts. A shunt is an accurate resistor that can pass a large current. When the current flows through the shunt, a millivolt-level voltage will appear at both ends of the shunt. So use a millivolt voltmeter to measure this voltage, and then the voltage Converted to current. The large current measurement is completed.

III. Methods

1．How to choose a shunt

(1) Select the rated voltage drop specification of the shunt according to the mV number marked on the dial of the ammeter (or current and voltage dual-purpose meter) used (usually 75mV or 45mV). If the ammeter used does not have this value, use the following formula to calculate the voltage limit of the table, and then select the rated voltage drop specification of the shunt.

The voltage limit of the meter (mV) = the current at full scale of the ammeter (A) × the internal resistance of the ammeter (Ω) x 1000

(2) Select the rated current specification of the shunt according to the current range to be expanded.

(3) Connect the two current ends of the selected shunt to the power supply and the load, and connect the potential end to the ammeter. Pay attention to the correct polarity of the ammeter terminals, and the range of the ammeter is expanded to the current calibrated on the shunt. value.

2．How to calculate

For motor test measurement, a current meter is often equipped with multiple shunts to solve the problem of ensuring the required measurement accuracy in a larger measurement range. At this time, it is required that the rated voltage drop of all shunts used is consistent with the current meter, such as 75mV. In this way, after the shunt is selected, the full range of the ammeter is the rated current value of the selected shunt, and the multiple of the ammeter (that is, the number of currents per grid on its dial scale) is the rated current of the shunt divided by the total number of grids on the dial scale.

There are slot type and non-slot type shunts for DC current measurement. The shunt has a manganese-nickel-copper alloy resistance rod and a copper strip and is plated with a nickel layer. Its rated voltage drop is 60mV, but it can also be used as 75, 100, 120, 150, and 300 mV.

Slot-type shunts have the following rated currents: 5 A, 10 A, 15 A, 20 A, and 25 A. Non-slot-type shunts are available in standard intervals from 30 A to 15 kA.

3. How to use a shunt

(1) Select the rated voltage drop specification of the shunt according to the mV number marked on the dial of the ammeter (or current and voltage dual-purpose meter) used (generally 75mV or 45mV). If the ammeter used does not have this value, use the following formula to calculate the voltage limit of the table, and then select the rated voltage drop specification of the shunt. The voltage limit of the meter (mV) = the current at full scale of the ammeter (A) × the internal resistance of the ammeter (Ω) x 10002. Select the rated current specification of the shunt according to the current range to be expanded. Connect the two current ends of the selected shunt to the power supply and the load, and connect the potential end to the ammeter. Pay attention to the correct polarity of the terminal DJ623-8 of the ammeter, and the range of the ammeter is expanded to the range calibrated on the shunt.

(2) How to connect the shunt

Generally, there are four bolts on the shunt, two large and two small. Two large bolts are used to connect the shunt in series to the circuit of the current signal to be measured. Two small bolts are connected to the signal input end of the instrument. Pay attention to the polarity of the signal. The end where the current flows into the shunt is the positive end and connects to the positive input end of the instrument signal input end; the end where the current flows out of the shunt is the negative end, and The negative input terminal of the instrument signal input terminal.

 How to connect the shunt

Instructions:

- Pin 1 is connected to the positive input terminal of the load signal under test (the positive terminal of the load does not need to be connected).

- Pin 3 is connected to the positive signal input terminal of the load (the wiring of the negative terminal of the load does not need to be changed).

- Pin 6 and Pin 7 are 4-20mA output for transmitting signal. Only models with (I) have this function.

- Pin 8 and Pin 10 are connected to 220V of the mains power supply, which is used as the power supply for the instrument itself (applicable in China, Hong Kong, etc.)

- Pin 9 and Pin 10 are connected to 110V of the mains, as the power supply for the instrument itself (applicable in Taiwan, the United States and other regions).

- When the measured signal is greater than 10A, an external shunt must be considered. For example, if you need to measure the current in the DC 50A range, the shunt specification that needs to be selected is 50A: 75mV.