NatTebb (Customer) asked a question.
P1AM Analog Input Precision
My team is trying to make a system with this PLC to track 2-3 analog inputs at 200hz. We recently learned the P1-4ADL2DAL-2 was never going to be able to keep up with that, so we're thinking about using the A0-A5 inputs on the side of the center module. But those inputs can only take 3.3V, our analog sensors run on 12V. We're willing to use voltage dividers to drop the voltage, but obviously we're now concerned if the P1AM will able to be able to read those sensors with the same precision AND range a 12v setup would be able to.
Also to be clear im a junior member of the team, so if something seems weird, please ask before castigating.
A challenging project. I agree with your concern. I believe you would not get the precision and accuracy you are looking for by adding a voltage-divider. You would be adding the accuracy, tolerance, temperature drift, etc. of the voltage-divider to the circuit. The P1AM-GPIO module you would be adding to the left side of the P1AM-100, connecting to the 3.3V "board-level" pins, has a 12-bit conversion (0-4095). The P1-4ADL2DAL-2 you listed has a 13-bit conversion (0-8191). The P1-04AD-2 has a 16-bit conversion (0-65535). This module would give the highest resolution, 152 uV/ count.
But, as you say, this input module cannot meet your requirement of 200Hz (5ms). Higher resolution needs more time to convert.
Not industrial, but could a 3.3V "board level" sensor fit your application? What is the update rate for the P1AM-GPIO? Besides the input conversion time, there is also controller scan time and sensor response time. (always a juggle between accuracy, precision, speed, and cost)
These "industrial-level" input modules have a 0-10VDC input range. I assume the 12VDC voltage you mention is the power supply voltage to power your sensors.
K Price
We're not thinking of using a GPIO module, i was referring to the ins on the side of the actual P1AM-100 ProOpen central module. These pins are usually occupied by the next module down the chain but can be accessed as general purpose IOs. Unless i'm missing something and we "need" the GPIO module you're referring to?
13 Bit precision is nice, but theoretically 12 bit resolution would be ok.
would an SPI analog to digital converter work for you I am thinking something like an LTC1856
I do not use analog very often so don't remember all the ins and outs of the modules, but I am wondering if you can disable unused analog channels in the modules? And if so, when channels are disabled does the whole module update rate also become lower?
My thought is that you could use a P1-04ADL-1 module which has an update rate of 2.5ms per channels and then disable the 3rd and 4th channels in order to get the update rate of the module to 200 times per second which would meet your tracking needs for the analog signal. Then just use a 2nd module in the same configuration when you need to use more channels.
Not sure if this is possible though, perhaps someone who uses these analog modules can confirm whether channels can be disabled or not and whether disabling the channel removes it from the scan update.
Right, I just assumed on the GPIO module because it provides the screw connections for field devices and, as you say, allows additional modules to be connected. Still some time is needed to do analog-to-digital conversion.
Anyway, I would either try to get sensors to match the 0-3.3VDC pin inputs, or preferably, get the input modules to match your sensor outputs.
Or, for the high-high-speed, move to a high-end (expensive) high-speed DAQ system. (Keyence is one vendor)
Not my normal mode-of-operation, but you could try the voltage divider idea. "One test is worth a thousand expert opinions!"
Our electrical team member is working on the voltage divider, will update if more questions come up or if this is relevant for someone else in the future.