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While often shielded, CAT5 can be of the UTP type, meaning unshielded twisted pair. The 'true' RS-485 cable you link to has two twisted pairs and a shield. If I remember right, CAT5e (and above) has a shield, at least most cables I have seen have - the exact standard can vary. I guess those would do the job just nice. Just make sure you use the twisted pair like in the original RS-485 cable (your data sheet looks like 1 White/Orange Stripe and 2 Orange/White Stripe are a twisted pair, and 3 Blue/White Stripe is a third, untwisted wire.)There seems to be a small impedance mismatch (100 Ohms for CAT5, 120 Ohms for RS-485).
This will cause reflections at the driver and at the receiver, but I am pretty sure your application will still work. While you may read that 120 Ohms is typical for RS-485, the termination network uses 120 Ohms between the differential pair and 2. 680 Ohms to VCC and GND.Thus, the value of the termination that the cable 'looks into' is smaller than 120 Ohms anyway: (120 (680+680)) Ohms = 110 Ohms.If you have the chance to test, you could go for it. I would probably not even hesitate and use STP CAT5(e). If your contract says you pay money for every minute your installation fails, you probably want to use cables with the proper specification. (The latter will still not make sure nothing ever fails, but you're probably in a better position if you can blame it on the 'true' cable instead of having someone else blaming your 'wrong' cable. But you see how this last paragraph has nothing to do with physics.).
Per reference to Maxim APPLICATION NOTE 3884from Jul 25, 2006 (cited 2104-05-28):mentions rs485 and cat5 with measurements.The performance of a Maxim driver (the MAX3469 in this case) and an equivalent driver from another manufacturer are presentedWhat Factors Limit the RS-485 Data Rate?The following factors affect how far one can reliably transmit at a given data rate:. Cable length: At a given frequency, the signal is attenuated by the cable as a function of length. Graphicus dt light font free download. Cable construction: Cat5 24AWG twisted pair is a very common cable type used for RS-485 systems. Adding shielding to the cable enhances noise immunity, and thereby increases the data rate for a given distance. Cable characteristic impedance: Distributed capacitance and inductance slows edges, reducing noise margin and compromising the 'eye pattern'. Distributed resistance attenuates the signal level directly.
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Driver output impedance: If too high, this limits drive capability.Receiver input impedance: If too low, this limits the number of receivers that the driver can handle. Termination: A long cable can act like a transmission line.
Terminating the cable with its characteristic impedance reduces reflections and increases the achievable data rate. Noise margin: Bigger is better.Slew rate of driver: Slower edges (lower slew rates) enable transmission over longer cable lengths.System designers often choose a driver and receiver from two competing manufacturers, but most designers are primarily interested in how far and how fast the RS-485 driver can drive a signal.
The performance of a Maxim driver (the MAX3469 in this case) and an equivalent driver from another manufacturer are presentedSignal integrity is tested by observing the driver's differential output. Set the oscilloscope to look for trigger points between the 80mV and -400mV thresholds.
(These thresholds are chosen because receivers have an input range of 20mV to -200mV, plus a noise margin.) Then, when pulses (bits) begin to 'run together', use eye patterns to determine the overall contributions of distortion, noise, and attenuation to the parameter called intersymbol interference (ISI).ISI forces you to reduce the bit rate to a level that allows an adequate distinction between pulses. Tests of the Figure 1 circuit show a consistent and clear correlation between trigger points and eye patterns. The eye patterns exhibit 50% jitter, measured using methods documented in National Semiconductor's application note 9774. Measuring jitter at 0V differential and ±100mV differential yields the data shown in Figures 4 and 5.Depending on drivers you get different resultAt 39Mbps and 340 feet of Cat5 cable, the driver output of Figure 2 exhibits an eye pattern in which signals cross in the middle of the eye—a condition indicating possible bit errors. The Maxim device at the same data rate, however, (Figure 3) shows no such condition. The Maxim transceiver offers better performance due to symmetrical output edges and lower input capacitance. The standard calls for a cable with an impedance of 100 Ohms at frequencies above 100kHz, DCR.
Twisted pair is twisted pair. So cat5 is 4 channels of rs485. It seems if there is a lot of RFI in the installation, shielded twisted cable can be justified.
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Rs485 is low impedance balanced, so twisting the pair helps with noise immunity as well as reducing the attenuation effect of higher baud rates due to the parallel capacitance of the wires in the cable jacket over the long lengths. These distances I'm talking about are greater than 100 meters.Now there was certain instances I used STP wire for rs485 because I had a lot of devices connected in a long run chain (DMX512 lighting fixtures). And the results before was a degraded signal that the devices near the end would interpret the signal incorrectly.unshielded cat 5 should work in your situation because of the voltage you will be running (5-10V) and your signal is not high frequency (above 500Mhz) in the first place.But You stated you are going to install this at a commercial setting, so it always better to use the worst case environment situations, and use shielded cable.I would insist also to shop around.
Beldon 3106A is what I typically use to wire balanced audio. Yes, it would work for that too, but 24 awg cable with plenum grade jacket is the standard.
From my experience with various HVAC controllers (Bacnet MSTP and Modbus), most of the time UTP cable works fine for short runs in low noise environments but can have intermittent and incredibly difficult to diagnose issues on long multidrop runs with differing equipment and incorrect termination.The labour involved in troubleshooting RS485 issues can quickly exceed the cost of using the correct cable.My advice is to be careful to use the correct cable and termination from the beginning or be prepared to replace the cable if it proves to be a problem.