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Maximum distance between sensors and PLC

Created by: ychervenkov at: 7/28/2009 12:28 PM (9 Replies)

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7/28/2009 12:28 PM	Rate (0)
ychervenkov Posts: 31 Rating: (0)	What is the maximum distance between sensors with analog output - 4-20 mA or 0-10 V and analog module for Simatic 224 or 226? How can I increase the distance on principle? Thanks Y Chervenkov
ychervenkov Posts: 31 Rating: (0)
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7/28/2009 12:47 PM	Rate (0)
naah Posts: 76 Rating: (8)	Hi, It depends on the cable diameter. To increase the cable length, increase the cable diameter! Good luck!
naah Posts: 76 Rating: (8)
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7/28/2009 1:45 PM	Rate (0)
Arunakat1 Posts: 217 Rating: (52)	Hi, Little bit more. Even the diameters are same size you can go more distance with 0-20 or 4-20 mA than 0-10V. Because current loop can go longer distance than voltage signals because voltage is dropping when distance increasing. Best regards.
Arunakat1 Posts: 217 Rating: (52)
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7/28/2009 1:50 PM	Rate (0)
Aristotelis Posts: 147 Rating: (34)	naah Hi, It depends on the cable diameter. To increase the cable length, increase the cable diameter! Good luck! Hi Y Chervenkov If you have a long cable, then the cable resistance is big. Recall the formula: R = l x ρ / A where R : electrical resistance l : conductor length ρ : specific resistance A : conductor cross section This means that the resistance of a cable is directly proportional to its length and inverse proportional to its diameter. If you want to send the signal over long range, the transmitter will have to spend more energy to keep the electron flow (i.e. the current) in the correct value, since the cable resistance (i.e. energy loss) has to be compensated. As suggested, you can increase the diameter - thus reducing the cable resistance - or find a way to measure how much power the transmitter is able to transmit. The SITRANS TH 400 has a Power output Po=12 mW, so you can derive how far it can transmit the signal. Also, it seems logical to assume that a transmitter that can get 120V DC supply voltage, is able to produce more power than a transmitter that can get 24V DC. Hope this helps Aristotelis
Aristotelis Posts: 147 Rating: (34)
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7/28/2009 1:54 PM	Rate (0)
ychervenkov Posts: 31 Rating: (0)	I'm understanding, but in the Catalog for S7 200 they are writed that for Analog modules the length of cable shilded is 100 meter maximum. My question is: "How I can increase this distance between the Analog module and senors with analog output - 4-20 mA or 0 -10 V
ychervenkov Posts: 31 Rating: (0)
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7/28/2009 3:40 PM	Rate (0)
Aristotelis Posts: 147 Rating: (34)	ychervenkov I'm understanding, but in the Catalog for S7 200 they are writed that for Analog modules the length of cable shilded is 100 meter maximum. Can you please be more specific where is this stated?
Aristotelis Posts: 147 Rating: (34)
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7/28/2009 4:32 PM	Rate (0)
ychervenkov Posts: 31 Rating: (0)	There are several sensors with analog output - 4-20 mA or 0-10 V, distributed of more than 100 metres from central station with S7 226. I want to connect them by analog module connected to the S7 Cpu 226. The distance is more thqn 100 m and this is bigger than maximum cable length, given in catalog for analog modules for S7 226. I don't know how I could this task. Purhaps it is not possible? Thanks
ychervenkov Posts: 31 Rating: (0)
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7/28/2009 5:55 PM	Rate (0)
Aristotelis Posts: 147 Rating: (34)	I am not able to find where this limitation (the 100m max) is stated in the manual, except for the RTD and Thermocouple analog modules. I think that this limitation is not valid for the other analog modules, since the distance depends solely on the transmitter and not on the module. It is out of the scope of the S7-200 manual to make assumptions regarding the nature of the transmitter one will use in order to send 4-20 mA to the analog module. If one possess a transmitter capable of transmitting 4-20 mA current in a long distance, i.e. 3 km, than one can use it without taking into account the 100m limitation. The current flowing through the cable - and thus arriving at the module - it would still reflect the appropriate value. If you happen to use RTD sensors, then I would recommend a different solution, like proper data communication via ProfiBus or - better yet - ProfiNet. Hope this helps Aristotelis
Aristotelis Posts: 147 Rating: (34)
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7/28/2009 10:42 PM	Rate (0)
Zunar Posts: 60 Rating: (6)	There are a number of 4-20ma transmitters and repeaters available on the market. Would using one of those devices work for your case?
Zunar Posts: 60 Rating: (6)
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11/29/2018 12:05 PM	Rate (0)
JenniferT Posts: 4 Rating: (1)	Now that's a pretty useful, thanks!
JenniferT Posts: 4 Rating: (1)
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