Is it better to connect the measuring element directly to a special module inside the PLC cabinet, or to connect it to a transmitter first before going into the PLC cabinet?
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It’s a common dilemma when purchasing instruments: should one choose a thermal resistor/thermocouple or an integrated temperature transmitter? Is it better to connect the measuring element directly to a special module inside the PLC cabinet, or to connect it to a transmitter first and then to the PLC cabinet? I’m not an expert; please explain the differences between the two methods. Let me first share my understanding: the integrated transmitter sends a 4-20ma current signal, so wouldn’t that result in less measurement error? The module measures physical signals, which seem to be voltage values; over long distances, it might be affected by the resistance of the compensation wires along the path It’s just that the transmitter needs to be connected to terminals, and these terminals are much smaller than the module, which helps save space inside the cabinet Another thing is that I don’t quite understand the cold-junction compensation for my thermocouple. In my opinion, the cold terminal connections are brought into the cabinet through compensation wires, but the temperature inside the cabinet can change with the outside temperature. How can we ensure the accuracy of the instrument readings? Regarding price, my understanding is that the cost of the module is much lower than that of the transmitter; using an integrated transmitter will result in a significantly higher cost. I’m not sure if my understanding above is correct; please help me out by correcting it if necessary.
If there’s a fierce tiger in the heart, it will dare to bite; if there’s a fat pig, it can eat meat. Use a local temperature control module for remote monitoring, or purchase an integrated temperature control unit. Refer to the post written by Ge. https://bbs.hcbbs.com/thread-1977228-1-1.html .
Temperature control modules aren’t expensive; they cost just a few dozen yuan. Those that are too costly are simply trying to overcharge people
Thank you for your support. I’ve read the post and would like to share my understanding. In my applications, I rarely choose the 3-wire system; I either go with the 2-wire system or the 4-wire system. Pure guesswork, just making things up. ;P Also, you mentioned in your post that installing on-site transmitters is a trend, but the reason for this is simply that it increases the errors in measurement over the length of the pipeline. The mass flow meters from Emerson that I bought before come in both split-type and non-split-type versions; I’m not sure which is better, but the accuracy specifications are the same in both cases. The most crucial point is that you didn’t provide a clear explanation for the question I raised in this post. Is my understanding correct, and what about the compensation issue for thermocouples?
It is better to connect the measuring elements directly inside the PLC cabinet, as the field environment is characterized by humidity, vibration, corrosion, etc., making maintenance difficult.
I’m not from the instrumentation field, so it’s a bit like talking to an elephant. :@ It’s best to learn* from Baidu now.
Thermal resistors can use a three-wire or four-wire configuration to compensate for the resistance errors of the cables. For thermocouples, compensation wires are used to lead them into the cabinet; the safety gates or modules inside the cabinet contain temperature sensing elements that compensate for any changes in temperature within the cabinet, so it’s not necessary to take temperature fluctuations inside the cabinet into account. However, compensation wires are expensive. If the operating conditions aren’t extremely harsh, an on-site temperature transmitter can be installed to avoid the need for compensation wires: D:D:D:D That’s all I can think of for now
1. If you ask specifically about thermocouples, then I will talk only about thermocouples and nothing else. 2. As for the on-site amplification of thermocouple signals, and temperature compensation, it is implemented on the circuit board of the temperature variation module! Only by providing warmth and nourishment on the spot can one truly nourish the body. Talking about the host computer as a means of providing reinforcement is complete nonsense! That was Hu Ji who planted the seedlings — Hu Qiu Bu. {:2_45:} 3. Has it been explained clearly this time? ........... To understand it better, go read another post written by my brother. https://bbs.hcbbs.com/thread-1635307-1-1.html
This post was last edited by A fierce tiger in the heart on 2019-7-31 15:27
The current understanding is that Baidu learns from its results; only when something can be explained clearly to a non-expert does it mean we truly understand it thoroughly
After taking a look, I understood it: there is another temperature sensing point in the temperature module, which can measure the temperature at the cold end. But I have another question: if the temperature module is supposed to be cheap, then this temperature measuring device probably isn’t very good. Wouldn’t it be stupid of me to spend a lot of money on a thermocouple that costs over 1000, and then add a module that costs just a few dozen dollars?