![]() Isolating the data acquisition device is a means of electrically separating signal source ground from the amplifier ground of the data acquisition device, as shown in Figure 4. This difference causes current to flow in the interconnection, which can produce offset errors. ![]() Ground loops are created when two connected terminals in a circuit are at different ground potentials. With isolation, you can avoid ground loops such as the one in Figure 3. A common method of preventing ground loops with a measuring data acquisition device is isolation. With the transducer selected, properly measuring the current signal is required to provide an accurate representation of the pressure applied to the transducer.Ĭhoosing a Current Measuring Data Acquisition DeviceĪn important aspect of building a current loop system is avoiding ground loops. To maintain transducer functionality, the voltage supplied should be no less than the minimum required likewise, supplying more voltage than the maximum specified can damage the transducer.įor the example current loop system, your chosen transducer measures pressure and has an operating voltage of 12 to 30 V. ![]() A voltage source provides power to the current-based transducer, allowing it to regulate the flow of current through the wires. Beyond the type of measurement (flow, pressure, temperature, and so on), an important consideration in choosing any transducer is the operating voltage. The first step in designing a current loop system is selecting a transducer. This example begins with determining an appropriate transducer for the application. A current measuring the data acquisition device provides an operator with feedback about the transducer measurements.Transducer is located 2000 ft away from the measurement device.System specifications include the following: To help better understand current loops, consider the design of an example system using a transducer throughout this white paper. An effective and accurate method of measuring current is to place a precision shunt resistor between the leads of the data acquisition device amplifier (in Figure 2) to convert the current signal into a voltage measurement to ultimately be related back to the transducer’s original measurement. The data acquisition device measures the regulated current flow. A 0 mA signal signifies a break in the loop. The transducer regulates the flow of current through the wires at 4 to 20 mA, where 4 mA represents a live zero and 20 mA represents the maximum signal. The DC power supply provides the power to the system. The main components of a current loop include a DC power supply, transducer, a data acquisition device, and wires connecting them together in a series, as shown in Figure 2. By using current signals and low impedance data acquisition devices, industrial applications benefit from better noise immunity and longer transmission cable lengths. Measuring current at any position along a single loop produces the same result. This is the basic principle on which a current loop operates. According to Kirchhoff’s current law, all current present at the beginning of a loop must reach the end. In theory, all current present at the beginning of a loop must reach the end as demonstrated in Figure 1.įigure 1. Kirchhoff’s current law (KCL) states that the sum of currents flowing toward a point is equal to the sum of currents flowing away from that point. However, these devices are sensitive to the noise induced by nearby motors, conveyor belts, and radio transmissions. You can use high input impedance devices to circumvent signal loss. For instance, the inherent disadvantage of using voltage to transmit signals in an industrial environment is voltage drops over long cable lengths due to wire resistance. While voltage-based transducers are sufficient in many environments, current-based transducers are at times preferred. This is in contrast to most other transducers, such as thermocouples and resistive strain gages, which use a voltage signal. Industrial-grade transducers commonly use current signals to transmit data. Using Current to Transmit Transducer Data
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