AB Analog in Question MicroLogix 2

[itsmoked]

I am just trying to confirm my understanding since the data sheet sure isn't!

The AB MicroLogix 4 channel analog input module.
-10V to +10V inputs.

Data sheet. (Takes about 10s)

http://literature.rockwellautomation.com/idc/groups/literature/documents/in/1762-in012_-en-p.pdf

It is my understanding that the sample rate is between 120ms and 450ms depending on a couple different filter qualities that are settable.

Q1: Is this the 'channel cycle time' or the 'A2D cycle time'? Another words, if I set a filter of 450ms will it take 1.8s to get an update on a particular channel? (One A2D multiplexed, or individual A2Ds?)

Q2: What happens if I read a channel multiple times in that 450ms period. Do I just get the same un-updated value back each time?

Q3: It is a 15bit A2D, (LOL). Does this mean that the resulting 32k values available shrink to 16k values if a region of 0-10V is used? (Presuming so.)

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[jde777]

Q1. No, I dont think that is correct.
Q2. Yes, I would agree with that statement
Q3. Even though it is 15 bit still uses the entire int or 32k, I think they just left justify it.

See calculation below:


First columb = Filter Frequency(Hz) Second Columb = Update Time(mSec) Third Columb = Channel Switching Time (mSec)
Forth Columb = Channel to Channel Reconfiguration Time mSec)
50 22 46 116
60 19 39 96
250 6 14 20
500 4 10 8




The module update time is the sum of the update times for all channels being used. If more than 1 analog channel is used the module update time for each channel is equal to the input update time plus the channel switching time. If all channels are not configured identically the channel to channel reconfiguration time must be added when switching between channels with different configurations. Therefore if 3 channels are used with a filter frequency of 60 Hz the module update time is equal to:

Module update time = (3) x 19 ms (input update time)
+ (3) x 39 ms (input switching time)
= 174 ms


If 3 channels are used with the following configurations:

Channel 0 +- 10V dc with 60 Hz filter
Channel 1 +- 10V dc with 500 Hz filter
Channel 2 4-20 mA with 250 Hz filter

The module update time is equal to:

Module update time = 19 ms (input 1 update time)
+ 39 ms (input 1 switching time)
+ 69 ms (channel to channel reconfiguration time)
+ 4ms (input 2 update time)
+ 10 ms (input 2 switching time)
+ 8 ms (channel to channel reconfiguration time)
+ 6 ms (input 3 update time)
+ 14 ms (input 3 switching time)
+ 20 ms (channel to channel reconfiguration time)
= 216 ms

If only 1 analog channel is used the module update time for each channel is equal to the input update time. Therefore if 1 channel are used with a filter frequency of 250 Hz the total update time is equal to:

Module update time = 6 ms (input update time)

 

[danw2]

>Q3: It is a 15bit A2D, (LOL). Does this mean that the resulting 32k values available shrink to 16k values if a region of 0-10V is used? (Presuming so.)

The table onpage 14 shows the bit positions in the data word.
which is a signed, 15 bit word, where 16th bit (bit #15) is the sign bit.

15 bits = 32K counts

0 to +10V = positive 32K counts
0 to -10V = negative 32K counts

It looks to me like you get 32K counts positive or 32K counts negative.

Dan

 

[itsmoked]

Thanks for the detailed responses guys.
Much appreciated.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com