Assembly line Timer/Speed control

Hello and thank you for taking the time to read my question. I'm a fairly new engineer so I'm sorry if my logic isn't as advanced as some of you.

I'm using a Micrologix 1000 PLC and programming with RSLogix 500

Here is what I'm trying to accomplish:
1. Piece of wood traveling on conveyor goes in front of photoelectric sensor.
2. Sensor activates and starts timing a timer.
3. If wood stays in front of sensor for a long enough time (lets say 3 seconds), timer outputs a done bit to a rung below that slows the speed of a previous conveyor.
4. I want to keep that done bit activated until the wood passes the sensor in a lesser amount of time than the timer is set for (say the wood passes the sensor in 2 seconds).

Problems:
I used a retentive timer (RTO) as the timer. That way if the timer is done, it keeps the conveyor at that speed and doesn't turn the done bit off when a gap of wood comes in between the sensor.

I want to be able to reset the RTO, I figured if I use a "less than" block with "source A" being RTO accumulated and it will reset if the accumulated value is less than the preset of the RTO. But I think it will automatically make the rung true once the timer starts timing.

I was wondering if there was another way to reset the RTO if the time it takes the wood to pass the sensor is less than the preset.

Thank you for taking your time to read my question. I'm sorry if I didn't go into enough detail and if you need me to explain anything else, please let me know.

I just figured out that the RTO retains it's accumulated value. I can't have that. So I'll use TON and an output latch. Now I just need to figure out how to activate the unlatch when the time is less than the TON preset.

Let's see if I can help by restating your application. let me know if I am wrong.

At the leading edge of each piece of wood start a timer.

At the trailing edge of each piece, if the timer is 'done' then set a bit to slow the preceeding conveyor. If the timer was not 'done' then reset this bit.

I have attached one possible approach.

In this application, I would probably avoid using the DN bits. I'd just have a TON timer with an impossibly high Preset value, e.g. 10 minutes. It'll never time out, and all you do is look at the ACC (accumulated time) value. If there's a piece of wood in front of the sensor, and Timer.ACC is greater than your "slow down" threshold, you slow the conveyor down.

Then if the next piece of wood clears the sensor while the Timer.ACC value is less than the speed up threshold, speed the conveyor back up. You'll just need to be careful of rung placement doing this - you'd need to put the comparison rung BEFORE the timer rung, or else the timer ACC will be reset before you can compare it. You may also need to use a oneshot to ensure it only does the compare at the instant the sensor turns off, and then doesn't do it again until another piece of wood appears.