Hi Andy, I thought you might reply! What I'm trying to do here is to go closed loop on my ballast tank control (I use a pumped air system). One of the things I would like to be able to do is to take on a fixed amount of water (during a dive for instance), and also to be able to perform small trim operations during the dive. The problem as I see it with a pressure system is that a) I already have one of those (used for depth control) but the response time is connected to how long it takes for the sub to settle at a depth (the sensor is not inside of the ballast tank). b) I'm not sure that it is accurate enough to repeatedly take on a fixed amount of water in the tank (I seem to be able to measure down to about 5/10mm of water with it). c) For closed loop I would really like something that gave a direct measure of the actual amount of water in the tank. I'm worried that the additional pressure from the depth the sub is at etc. is going to complicate things rather a lot. I had thought about using the depth sensor for this (and maybe moving the sensor into the tank to do it). But I'm concerned with the effects on the closed loop of the lag that you get between taking on water and the sub actually moving to a depth. Maybe if I move the sensor I won't have this problem (since it would be inside of the tank?). But I guess I would still have the problem of sensitivity/accuracy. Just a quick note here. The way I like to run my subs is not to spend ages ballasting them so that taking on a full tank of water takes them to a neutral buoyancy (which is what most people do). Instead what I would like to do is to automate this part so that I can just do a simple pond side set-up of taking on water until the sub is neutral then store the value associated with this state in eeprom. Then I just command the sub to take on the same amount of water when I dive. I currently do this open loop (timing based) but this tends to be a bit hit and miss as the batteries go down... Andy ----- Original Message ----- From: "Andrew Kunz" To: Sent: Monday, October 16, 2000 4:09 PM Subject: Re: [EE]: Help water level > Andy, > > What's the purpose of measuring the water in the ballast tank? > > Given the initial volume of air (which I hope is constant in your situation), > the volume of water will change as the air pressure changes (or vice versa, > depending on your field of view). So a pressure-based system should be > adequate. And the pressure will exactly correspond to sub depth. > > Why not use one of Skip's ADCs? > > Andy > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > > > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.