Hey there, I'm curious to hear your insights on Thermocouples and how long you can run them without accuracy issues. At my plant, we have 12 T/Cs with approximately 300 Ft runs using type K and 16AWG Type K extension cable. I plan on replacing the extension T/C cable with a shorter run and connecting it to a hart card to scale the mV to a 4-20 signal before sending it to my PLC. The T/Cs have never been accurate since I started working here, so I'm unsure if it's a design flaw or insulation degradation over time due to heat. I'd appreciate any thoughts or advice you may have on this matter.
When considering replacements for long stretches of T/C extension cable, opting for current loop transmitters in an industrial setting is a wise decision. If you're experiencing issues with inaccurate temperature readings from your T/Cs, it's worth examining whether there are any AC power conductors near the extension cable that could be causing interference. The magnetic field produced by high voltage AC power conductors running parallel to the T/C extension cable has the potential to induce voltage, leading to signal noise. For example, I once encountered communication errors when a 20 ma Current Loop RS232 serial communication cable was placed in close proximity to a 480 VAC 3 Phase 60 Hz track for a hoist. During operation of the hoist, voltage discrepancies between communication bits were observed on an oscilloscope, dropping below the threshold for accurate data transmission. This highlights the importance of proper cable routing and isolation to prevent external interference from impacting signal quality.
While working in the food industry, I came across solutions for managing noise issues on RTDs and thermocouples with lengthy wiring setups. These temperature sensors and transmitters from AutomationDirect proved to be an effective fix: TTD-20-N40300F-H, RTD1-25N-150-H, and XTH-01500F-K. These products are designed to enhance temperature measurement accuracy in industrial environments.
OldChemEng recommended replacing the lengthy T/C extension cables, opting for current loop transmitters in industrial settings for improved accuracy. Delving into the issue of inaccurate temperature readings from the T/Cs, he queried the proximity of high-voltage AC power conductors running parallel to the T/C extension cables. The magnetic field generated by these AC power conductors may lead to noise interference by inducing voltage in the T/C extension. Drawing from personal experience, he shared a scenario where parallel placement of a 20mA Current Loop RS232 serial communication cable next to a 480VAC 3 Phase 60Hz track caused communication errors when operating a hoist. Despite the shielding of the T/C cable and all AC conductors being Teck cables, the question of whether this adequately mitigates electromagnetic interference remains unanswered. Nonetheless, these measures should provide some level of protection. Thank you for sharing your insights.
I have observed Type K runs up to 400 feet without any problems using a 12 pair 20 AWG extension cable with an overall shield. Have you checked the accuracy of the Hart module and confirmed the TC accuracy at the connection point to the Hart module?
OkiePC shared a helpful solution I discovered in the food industry to address noise problems with RTDs and thermocouples over long wiring distances. I found these temperature transmitters and sensors from Automation Direct to be effective: TTD-20-N40300F-H, RTD1-25N-150-H, and XTH-01500F-K. I appreciate the recommendation and will explore these options further. Currently, I am using an EandH Hart transmitter TMT72.
It sounds like you're dealing with some notable issues related to the thermocouples and accuracy. Thermocouples indeed lose their accuracy over time due to a phenomenon known as 'drift', especially when they are exposed to high temperatures, corrosive environments, or mechanical stress. I'd start by checking the physical condition of the thermocouples and the insulation material on your extension cables for any signs of degradation. But your plan of shortening the cable run, converting mV to a 4-20 signal, and delivering it to your PLC sounds promising. It's important to remember that the length and type of extension cable can affect the measurement accuracy drastically. Also, consider calibrating your T/Cs as part of routine maintenance to counteract any potential drift. Do keep us posted on your progress!
It sounds like you're dealing with quite a challenging situation with your Thermocouples. First, it's worth noting that thermocouple accuracy can indeed degrade over time, especially if often exposed to high temperatures. Environment-related stress can cause insulation breakdown over time, leading to measurement errors. The length of the thermocouple cable can also impact reading accuracies due to resistance in the wire — your plan to shorten the run sounds like a good idea. Converting the signal to a 4-20mA signal as close as possible to the thermocouple will reduce potential errors due to electrical noise. If you haven't done so already, it may also be beneficial to calibrate your T/Cs. Regular calibration helps ensure the ongoing accuracy and reliability of thermocouples in your systems. Just remember to control for cold junction compensation in your new setup. Good luck with your project!
From my experience, Type K thermocouples are generally reliable but accuracy issues can arise due to various circumstances. Degradation of insulation, as you mentioned, can affect their precision, especially if the cables are exposed to harsh conditions for a long period of time. Before you invest in replacing the cable, I would suggest verifying the accuracy of your T/Cs with a good calibrator. Also, considering the long cable runs at your plant, there may be a voltage drop across the extension wires which could result in reading inaccuracies. Transmitting a 4-20mA signal from a Hart card is a smart and common solution for minimizing these types of errors, especially over long distances. However, make sure your chosen Hart card features good quality signal isolation to avoid ground loop issues. I hope this helps!
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Answer: - To optimize Thermocouple accuracy for long distance installations, consider using shorter cable runs, utilizing signal conditioning devices such as a hart card to scale the mV to a 4-20 signal, and ensuring proper insulation to prevent degradation over time due to heat.
Answer: - Factors that can affect Thermocouple accuracy over long distances include cable length, cable type, signal interference, insulation quality, and signal scaling methods.
Answer: - To troubleshoot inaccurate Thermocouples in your plant, consider checking for design flaws in the installation, inspecting the condition of the cables for insulation degradation, and verifying the calibration of the Thermocouples. Additionally, using signal conditioning devices can help improve accuracy.
Answer: - Using Type K Thermocouples with 16AWG extension cable for long distance installations can lead to accuracy issues due to signal losses and interference. It is recommended to use shorter cable runs and proper signal conditioning methods to improve accuracy.
Answer: - To ensure accurate temperature readings from Thermocouples connected to a PLC, consider implementing proper signal conditioning devices,
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