BCMaint (Customer) asked a question.
Panel meter vs Analog input
We are currently retrofitting a machine with a PLC. It currently uses a linear potentiometer with the DPM3-AT-4R-H panel meter to determine position. Would scaling 0-10v using an analog input card be as accurate and fast? Total travel is around 12 inches and the display is currently read as xx.xxx. Also if we use analog input, what is the difference between 16,13 and 12 bit?
Thank You
In analog-to-digital conversion (ADC), the bit depth determines how finely the analog signal is divided into discrete digital steps. Here's how 12, 13, and 16-bit compare:
Resolution (number of steps)
Bit Depth
12-bit 4,096
13-bit 8,192
16-bit 65,536
Each additional bit doubles the resolution. So going from 12 to 13-bit doubles your precision, and going from 12 to 16-bit gives you 16× more resolution.
In short: more bits = finer granularity = ability to detect smaller changes in your signal.
Just to add a little bit extra information here for the OP:
Just because you double your resolution each bit you go up, doesn't necessarily mean you want to always keep going up. You need to think about how accurate your analog signal is as well as the noise on the signal lines from interference of nearby electrical sources. If a potentiometer for example is rather low grade, then on 12 bit you may have a perfectly steady signal at exactly where you set it, 13 bit may have a tiny bit of jitter where the signal "at rest" for your set point is moving up and down a few counts and you need to use a quick averaging filter to eliminate this jitter. A 16 bit with the same pot may jump around by +/- a thousand counts and require a much longer averaging filter to keep the signal steady.
I'm not saying this WILL be the case with your plan, I'm just saying you need to take into account how much resolution you actually need, the quality of your analog device, and how much care you have taken to both your device generating the analog signal as well as keeping analog signal lines away from interference.
More doesn't always equal better.
So even though the DPM3 looks faster at 50 ms vs. 80 ms, the P2-08AD-2 wins per channel by a wide margin, and is far better suited for control. The DPM3's slower Sigma-Delta approach is an advantage when signal quality and display stability matter more than speed.
Yes, a lot of specs to look at. The good news is that you are retrofitting, so you can look at lots of control and sensor options, and you're going to a PLC, which provides all kinds of control options. Different PLCs allow for different control options. (For example, I love the Stage programming of the Do-more PLCs for sequential-type control.) You asked if analog would be accurate and fast. Pot-type linear sensors can have a resistance tolerance of +/- 20%. This could be a large source of error if not calibrated out. If your linear motion is from a rotary drive, you could consider rotary encoders (incremental with pulse outputs, 1-turn absolute with gray code output, multi-turn absolute with comm. outputs, etc.). For linear motion (in addition to the pot type), ADC carries draw-wire and inductive type sensors with analog output. If noise is a problem, as mentioned in previous post, and you're going with the analog signal, consider going with 4-20ma, rather than 0-10VDC.