4-20 mA Current Loop Basics. Sensors or other devices with a 4-20 mA current loop output are extremely common in industrial measurement and control applications. They are easy to deploy, have wide power supply requirements, generate a low noise output, and can be transmitted without loss over great distances.
What is the transmitter?
A transmitter (or radio transmitter) is an electronic device which produces radio waves with the help of an antenna. A transmitter generates a radio frequency current applied to the antenna, which in turn radiates radio waves.
Loop calibrators are a type of electrical calibrator specifically designed to troubleshoot 4-20 mA current loops. Current loops are used to measure pressure, temperature, flow, pH, or other process variable. A current loop can also be used to control a valve positioner or other output actuator.
The HART Communication Protocol (Highway Addressable Remote Transducer) is a hybrid analog+digital industrial automation open protocol. Its most notable advantage is that it can communicate over legacy 4–20 mA analog instrumentation current loops, sharing the pair of wires used by the analog only host systems.
The crankshaft position sensor measures the crankshaft position and speed.
- Step 1 - Test the Voltage Output. To test if it your crankshaft position sensor is working properly, you have to test the voltage output.
- Step 2 - Wiring the Voltameter.
- Step 3 - Set the Multimeter.
- Step 4 - Set the Meter.
The range switch on the front of the multimeter shows the maximum current that can be measured on that range. The range switch is pointing at the "200m" DC Amps range in the picture. Therefore, the full-scale readout for this range will be about 200 milliamps.
A live zero is a loop signal where the zero value is some number higher than zero. 4-20 mADC, 1-5 VDC, 10-50mV, etc., are all examples of live zero. A dead zero is where the zero value of the signal is itself the zero value of the loop.
Everybody knows that loop checking and field instrument testing is the last piece of the puzzle in each project before commencing the commissioning of any system. Each contractor or company has its own procedure and common practices for instrument loop checking and functional testing.
The output signal(4-20ma) is returned on the same wires that powers it. the main purpose of this design is to reduce wiring cost, standrdisation of circuits, and above all, to keep all the transmitters at same ground potential. A 4 wire inst. has design flexibility to utilize any power like, 230vac, 24 vdc or 110 vac.
- Always test your meter first!
- Determine the amperage rating for your digital multimeter.
- Select the appropriate function on your multimeter.
- Set the range on your multimeter.
- Plug the leads into the appropriate terminals.
- Run the circuit through the multimeter to measure the current.
Definition of: 4-20 mA. 4-20 mA. (4 to 20 MilliAmp) A point-to-point or multi-drop circuit mainly used in the process automation field to transmit signals from instruments and sensors in the field to a controller. It sends an analog signal from 4 to 20 mA that represents 0 to 100% of some process variable.
TRANSMITTER FEATURES. Transmitters provide a two-wire output with the same wiring used for power and output. The load resistance is connected in series with a dc power supply, and the current drawn from the supply is a 4-20 mA or output signal which is proportional to the input signal.
To measure current, you must connect the two leads of the ammeter in the circuit so that the current flows through the ammeter. In other words, the ammeter must become a part of the circuit itself. The only way to measure the current flowing through a simple circuit is to insert your ammeter into the circuit.
Also, a 0-10V signal is susceptible to voltage drops caused by wire resistance, especially over long cable runs. A 4-20 mA or 0-20 mA signal, on the other hand, offers increased immunity to both electrical interference and signal loss over long cable runs. The same can not be said for a 0-10V sensor.
For serial communications, a current loop is a communication interface that uses current instead of voltage for signaling. Current loops can be used over moderately long distances (tens of kilometres), and can be interfaced with optically isolated links.
Loop powered devices are electronic devices that can be connected in a transmitter loop, normally a current loop, without the need to have a separate or independent power source. These devices are designed to use the power from the current flowing in the loop.
A passive output means the flowmeter is externally powered. An active output means the flowmeter is internally powered such as 4 wire device. It appears you are asking about a pulse output. An analog such as 4-20mA signal would be the same passive = external and active = internal power.
Current loop. A major application of current loops is the industry standard 4–20 mA current loop for process control applications, where they are extensively used to carry signals from process instrumentation to PID controllers, SCADA systems, and programmable logic controllers (PLCs).
Signal ground is a reference point from which that signal measured, due to the inevitable voltage drops when current flows within circuit, some 'ground' points will be slightly different others it protective connected earth. Chassis ground vs signal.
A few multimeters have illuminated displays for better viewing in low light situations. The selection knob allows the user to set the multimeter to read different things such as milliamps (mA) of current, voltage (V) and resistance (Ω). 10A is the special port used when measuring large currents (greater than 200mA).
Every inline series-connected ammeter, including a multimeter in a current range, has a certain resistance. Most multimeters inherently measure voltage, and pass a current to be measured through a shunt resistance, measuring the voltage developed across it.