In the process of upgrading a 4-20 ma system, we are transitioning from a traditional circular paper chart recorder to a modern Bluetooth receiver for the 4-20 signal. This Bluetooth receiver effectively transmits the 4-20 ma input data to the cloud via the internet. Aside from configuring the receiver for a 4-20 ma input range (4 ma minimum and 20 ma maximum), are there other factors to consider such as the impedance of the current leg? Can the new receiver be integrated in series with the existing system? Will any additional calibration be necessary for this setup?----------------------------------- Barry -----------------------------------
Hello Barry, In response to your query: Numerous Industrial Process Transmitters (4-20mA) have a maximum loop resistance of around 750 ohms. It is permissible to connect additional devices within this loop, provided that the transmitter's loop resistance limit is not exceeded. This information can typically be located on the Transmitter dataplate or in the Manufacturer's Manual. I trust this information proves helpful. Best regards, Charles Palmer. If you are retrofitting a 4-20 mA system to replace a circular paper chart recorder with a Bluetooth receiver for the 4-20 signal, there are factors to consider. Besides configuring the receiver to support a 4-20 ma input and stream data to the cloud via the internet, you should also take into account the impedance of the current leg. Additionally, it may be feasible to integrate the new receiver and the current system in series, but be sure to check if different calibration is necessary. Thank you for your inquiry. (Keywords: Industrial Process Transmitters, 4-20mA system, loop resistance limit, Manufacturer's Manual, impedance, calibration)
In addition to my earlier response, Barry, it is important to note that a 4-20mA transmitter is typically powered by a 24v DC source (such as a PLC or DCS) with a 250 ohm resistor across the input terminals. This resistor converts the current signal (4-20mA) into a voltage signal (1-5V) for the PLC or DCS. It is crucial to factor in this resistance along with other devices in the loop to calculate the total loop resistance effectively. Regarding your inquiry about retrofitting a 4-20 mA system with a Bluetooth receiver, it is essential to consider the impedance of the current leg. While setting the receiver to 4-20 0 (4mA minimum and 20mA maximum) is necessary, you may also need to ensure proper calibration when integrating the new receiver with the current system in series. ------------------------------ Charles Palmer
After gaining a better understanding of how it functions, I now see that the sensor will transmit a 4-20mA signal irrespective of the input voltage as long as it provides enough power to overcome the impedance of the connected parts. In response to the previous message regarding the 4-20 MA Pressure Sensor, keep in mind that a 24v DC source typically powers the 4-20mA transmitter, incorporating a 250 ohm resistor across the input terminals to convert the current to a 1-5V voltage signal for the PLC or DCS. To calculate the total loop resistance, one must consider this added resistance along with that of all other devices in the loop. When setting up a Bluetooth receiver for the 4-20 signal to replace the paper chart recorder, aside from configuring the receiver to accept 4-20mA input, you should also take into account the impedance of the current path. It may be possible to connect the new receiver and the existing system in series, but calibration adjustments may be necessary.
Indeed, that is accurate. When powered by 24v DC, the transmitter generates a current that represents the Process Measured variable and flows through the circuit. One potential issue could arise if the 24v DC supply is below normal and the resistance is near the 750 ohm limit. In such a scenario, there might not be enough Voltage force for the current to flow properly, leading to a lower reading on the receiver (PLC or DCS) than the actual value. These factors can be easily confirmed using a Digital Multimeter if any errors are suspected. Trust this information proves beneficial. Thank you, Charles. Charles Palmer Barry Busey Regarding the use of a 4-20 mA Pressure Sensor, it is crucial to understand that the 4-20mA transmitter typically operates on a 24v DC supply (PLC, DCS, etc.) with a 250 ohm resistor connected across the input terminals. This resistor converts the current range (4-20mA) into a Voltage signal range (1-5 V) for input to the PLC or DCS. Therefore, the overall loop resistance includes this resistance along with that of other devices in the loop. This knowledge is essential for accurate operation and calibration of the system.
Definitely, thank you once again! Barry Busey here checking in. I wanted to confirm the details about the 4-20 MA Pressure Sensor. When the transmitter is powered by 24v DC, it generates a current that represents the Process Measured variable and flows through the circuit. One issue that may arise is if the 24v DC supply is lower than normal and the resistance is near the 750-ohm limit, there might not be enough voltage for the current to flow properly, resulting in a lower reading on the receiver (PLC or DCS) than the actual value. You can easily verify all these parameters using a Digital Multimeter if needed. I hope this information is helpful. Best regards, Charles Palmer.
Hi Barry, it's great to see that you're staying on top of technological advancements by considering such an upgrade. Aside from what you've already mentioned about the input range, you should definitely consider the impedance in your implementation. You want to ensure the receiver impedance doesn't overpower your overall loop resistance. On the point of integration, ideally, the new receiver should be able to integrate in series with your existing loop, maintaining the open-circuit philosophy. Regarding calibration, it will largely depend on the precision with which the receiver deciphers the 4-20mA signal. It wouldn't hurt to perform a calibration check post-installation to ensure accurate signal conversions. Keep in mind to account for both device and system response times to ensure real-time data monitoring.
Absolutely, Barry, impedance of the current loop is a key factor to consider. You need to ensure your Bluetooth receiver is capable of handling the loop's resistance, which may vary based on cable length/quality and the devices connected. Also, remember, although it's digital, it will inevitably incur some form of data latency, so consider the acceptable delay in your case. Integrating in series with the existing system is plausible but you’ve to check if the new receiver requires isolation. About calibration, while modern sensors and receivers are usually calibrated by the manufacturer, it's always a good practice to recheck the calibration in your specific use environment to achieve most accurate results. Let's not forget the importance of power reliability and data security while transmitting the data to the cloud as well.
Great points, Barry! You definitely want to consider the impedance of the current loop to ensure that the Bluetooth receiver doesn't impact the overall function of your system; it should be low enough to maintain accurate readings without causing signal drops. Integrating the receiver in series with the existing system is typically standard practice, but double-check the manufacturer's guidelines to avoid any electrical losses. As for calibration, you might need to perform some adjustments after installation to fine-tune the readings, especially since digital instruments can have different sensitivities compared to analog ones. Also, keep in mind the potential for interference when transitioning to cloud capabilities—testing in real-world conditions will be key!
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Answer: Answer: When upgrading, it is essential to configure the receiver for the 4-20 mA input range and consider factors like the impedance of the current leg. Integration with the existing system and the need for additional calibration should also be taken into account.
Answer: Answer: The Bluetooth receiver effectively transmits the 4-20 mA input data to the cloud via the internet, enabling remote monitoring and data storage.
Answer: Answer: It is important to ensure that the new Bluetooth receiver can be seamlessly integrated in series with the existing system to maintain functionality and compatibility.
Answer: Answer: Depending on the specific setup and requirements, additional calibration may be necessary to ensure accurate and reliable data transmission and monitoring.
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