Logix5000 - TOT error?

First time trying to use the TOT function block.
I have a Doppler radar reporting the speed of my equipment, so I want to know how far it has travelled.

My process will run for 30min avg, up to an hour at a time.
Process runs at about 10mph.
That means total of 5 miles, to 10 miles total.
My Doppler radar will report in ft/s, and I want the units of ft.

At every 50ft increment, I want to run part of my process.
Question: Over 25000ft, what sort of error will the TOT block have?

My other option is to run timers that will process for no more than 10sec to trigger the process. I like the idea of being able to measure the DISTANCE traveled, rather than infer based on a timer.

10 mi/hr is 14.66 ft/sec. Even if you take a reading every second and just add the reading to your total you can be off up to that amount. Or you set a window of about 43 feet to 57 feet and process the total if it's in there. How often does the reading from the radar update?

bernie_carlton said:

10 mi/hr is 14.66 ft/sec. Even if you take a reading every second and just add the reading to your total you can be off up to that amount. Or you set a window of about 43 feet to 57 feet and process the total if it's in there. How often does the reading from the radar update?

Click to expand...

Radar is 4-20mA, 0.8-480 km/h +/- 0.34% @ 1km/h (+0.0014% per 1km/h)

The overall length is not a concern, I mis-stated that.
The sample will be taken as "Current Total Distance" then "ADD 200ft" and compare when "Current Total" > "ADD 200ft Total"
Question v2: How accurate will the TOT be over 15-20 second measurements?
I haven't found anything in the LitLib about the TOT function... Anyone know what document I can find it in?

Typically when I have made my own totalizers, I find that they can be out +/-5%. Because of this, we use HSC for measurements of volumes and take the total pulses at the end, and use that for an accurate measurement.
In this scenario, I am stuck with a 4-20mA to measure speed, because I can't run an encoder.

My guess is that your question is quite complicated to answer. It will depend on:

Accuracy of sensor
Precision of 4-20ma from sensor
Precision of 4-20ma of PLC input
Update rate of sensor
Update rate of TOT and PLC
Amount of Accel/Decel involved (accuracy is maximized when speed is absolutely constant)

You will need to choose a timing mode for the TOT - period/oversample/real-time. You sensor and 4-20 response should be 5-10 times faster that the selected timing rate.

I'd say that you are best to build it and test it out.