What is a 4-20 mA data logger?
The term 4-20 mA data logger covers data loggers that are equipped with a standardized current interface (inputs and outputs). 4-20 mA data loggers are used in environments where high interference levels prevent precise and reliable transmission of measured values. Data loggers 4-20 mA are also a reliable alternative to data loggers with high-impedance voltage inputs when measured values are transmitted by cable over long distances. In this article, you can find out exactly what the advantages of the 4-20 mA interface are.
Reliable signal transmission in an increasingly electrically active environment
Interference-free transmission of signals plays a central role in measurement technology. In analog data transmission, which is common in data loggers, measured value signals are transmitted with the smallest voltages or currents. In our increasingly "electrified" environment, more and more interference factors are active that can falsify measured values:
- High-performance digital systems with high transmission frequencies
- Electrically operated components, for example drive motors
- Directly mains operated contactors
- Electrostatic discharges
- Wireless control or communication devices
Data loggers usually process electrical analog signals when sensors are used for physical variables. Analog" refers to electrical signals that can assume any value between a minimum and maximum value. The signals are transmitted from the source, the sensor, via electrical conductors to the target device, the data logger. In accordance with DIN IEC 60381-1, these electrical signals are standardized and referred to as standard signals:
- Current signal 0 mA - 20 mA
- Current signal 4 mA - 20 mA (offset zero, with offset zero point)
A standard has also been defined for voltage signals. The following voltage signals are listed in DIN IEC 60381-2:
- <0V - 5V
- 0V - 10V
- 1V - 5V (offset zero point)
- 2V - 10V (offset zero point)
- -10V - 10V (optionally with or without offset zero point)
With a 4-20 mA interface on a data logger, measured values can be easily transmitted over longer distances than current signals. With current transmission, internal resistances and therefore voltage drops in the cable are irrelevant as long as the voltage is sufficient. The current of the measured value is sufficiently high compared to the interference currents, so that precise interference-free transmission of the measured values is guaranteed.
What are standard signals?
In order for physical process variables, such as temperatures, humidity or pressures, to be processed by evaluation devices, they must be converted into standardized electrical signals. These signals can be transmitted either as current or voltage signals.
In the vast majority of applications, current signals are preferred to voltage signals. The advantage of current signals is their insensitivity to electromagnetic interference. Voltage losses due to line resistances are also not to be expected with current signals.
Advantages of current signals with offset zero point
In industrial environments, signals with an offset zero point, for example 4-20 mA, are primarily used. Here, an electrical signal that deviates from zero is assigned to the start of the measuring range. Working with an offset zero point offers two advantages:
- The offset zero point (zero point = 4 mA) allows cable break monitoring tasks to be implemented. If a signal is present that is below the zero point (e.g. 3 mA), a fault or cable break can be safely assumed.
- With the 4-20 mA current unit signal, the signal circuit has a permanent power supply. The available energy can be used by the transmitters used for their own power supply. Therefore, only 2 wires are required to the sensor.
Standard signals allow great flexibility in the field of measurement technology
Data loggers that process standard signals offer a wide variety of sensors in practical applications. The Delphin data loggers allow the use of the following external sensors, among others:
- Temperature sensor
- Humidity sensors
- Vibration sensors
- Force sensors
- Water level sensors
- Pressure sensor
- Flow sensor
- Any type of external analog sensors
Reliable protection against overvoltage is standard with our data loggers
When using data loggers with analog inputs, for example 4-20 mA data loggers, the measurement results may be distorted due to ground potential differences. For this reason, Delphin Technologies consistently installs galvanic isolation in all data loggers. Galvanic isolation keeps the electrical potentials permanently separated from each other and the circuits practically potential-free. The sensitive hardware is thus reliably protected against overvoltage - and the measurement results remain reliable at all times.
4-20 mA data logger: A clear plus, even with existing control systems and PLCs
Analog signals can be recorded not only by data loggers, but also by controllers and PLCs. However, when it comes to increased signal sampling resolution and significantly improved measurement speeds, data loggers such as the Delphin are ideal Expert Logger ideal as a supplement to existing systems. Speeds and sampling rates play a key role, particularly for demanding measurement tasks, for example in the context of vibration measurements. We would be happy to advise you in detail on the many possibilities offered by the use of Delphin data loggers. Why not give us a call right now!
How do you actually choose the right 4-20 mA data logger?
When selecting the right 4-20 mA data logger, a number of factors must be taken into consideration. In addition to the main criteria of sampling rate and speed - which must exactly match the respective measuring task - the following factors should also always be taken into account:
- How does the data logger ensure long-term measurement reliability?
- Does the data logger offer galvanic isolation to protect against overvoltage and ensure reliable, high-precision measurement results?
- Is the number of available analog inputs and outputs sufficient for the measurement tasks at hand?
The converted costs per analog input are often one of the strongest criteria for or against a 4-20 mA data logger. This is where Delphin Technology comes in with flexible scalability of the available analog outputs and analog inputs. The Delphin 4-20 mA data loggers can be expanded as required using expansion devices. This means that there are always enough connection options for sensors, even for the most extensive measurement tasks. The system is supplemented by the database or DAQ measurement data software Delphin Data Center. The Delphin Data Center can be used to record a large number of analog signals from several data loggers distributed in the measurement network as well as from third-party hardware such as a PLC controller. This means that even large quantities of measurement data can be recorded decentrally without having to route the data via long cables to just one data logger.
Would you like to find out more about the Delphin data loggers or do you have a specific measurement task that you would like to discuss with our experts? Just give us a call! We look forward to inspiring you with the Delphin products soon!
The right software for your measurement and testing solution
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