Programmable or Pre-Set Oscillating Timer Circuit

How much room are you talking?

I can come up with a couple of Ideas that may take up too much space.

I have an inside diameter in the steel housing of 1.25" and it should only be around 24" long so I should have plenty of room. Another steel housing that holds the batteries will thread onto this section and both will be sealed so oil,gas,water, and pressure don't see any of the components. This tool will be ran in oil/gas wells to trigger oilfield explosives. Battery power enters the timing circuit and has to stay at 0 on the output until timer opens or closes depending on which way it is wired. The point is for me to have enough time to get the explosives to the right depth before they fire, so that's why I need a 0 volt output until the timer hits its mark. This will be one of 4 safety features on the tool but the others will be mechanical safety barriers consisting of temperature and pressure switches to prevent firing on surface. thanks for your comment

Something doesn't sound right about this. What actually initiates the detonation? If it's a signal sent down wires from the surface, surely it would be better to keep any safety circuitry up the top, where it's nice and clean and cool.

(Don't know that you'll find any kind of safety-rated timer to work in that envelope and with that temperature range anyway).

You can keep in all the temperature & pressure switches, but if it can't fire without a signal from the surface, why not just run a pair of wires down? Short or open circuit would not initiate premature detonation.

Confess I know bugger-all about dropping stuff down boreholes (tho' I've done a little work on high temp. down-hole electronics).

Not trying to put a downer on you, or be contentious.Please enlighten me.

This isn't new to me, I've been doing this for 3 years and is common practice in the oil/gas industry. We work at depths normally around 10-15,000 feet so you can't initiate anything from surface in this application. I don't need a safety rated timer, just one that has one output that can be set to give me approximately 12 volts dc once the timer hits its mark. There will be a firing pin on the bottom of the tool that initiates an electric detonator causing the explosive train to set off. These tools are hoisted down the hole on stainless steel line that is normally .108" - .125". I just wanted a recommendation on which style timer to use that is all.

OK, thanks. I'll think some more.

Would you be able to use a timer switch designed for normal 110 VAC / 60 Hz in a circuit with a 12 VDC power supply plugged into the circuit? You can buy an inexpensive bathroom fan controller switch that can be set for 10, 20, 30 and 60 minute intervals. The cable from the 12 VDC supply could then be run into your steel housing that is subjected to the high temps. Perhaps automotive engine cables are rated for 300 F operation (?).

The problem is the size of the housing. This will be an oilfield application and the tool's outside diameter is 1 3/8" stainless steel leaving the inside diameter roughly 1.25". Length doesn't really matter but I'm aiming at 24" for the entire circuit. I'll want to apply 12vdc battery power to the timing circuit and for sure have 0 volts on the output until the switch opens or closes, which ever way it is setup on the output. So just think of it as one section of a tool that will be housed in steel that attaches to another steel housed battery section that will thread together and be sealed with double O-ring connections. It has to be enclosed so oil/gas/water/ pressure does not see the components.

How about a mechanical timer that closes a switch?

I agree. What guarantees that the device will reach its intended destination at any certain time? I envision the device hanging up in the hole, the timer timing out, and kaboom!

what exactly are you agreeing too? You clearly know nothing about this application so the best thing you could do would be to stay quite. There is a reason that the teacher gave you that pointed hat with a big D on it when you were in school (probably the one and only day you actually went to school)

I appreciate your vote of confidence. I've been doing this line of work for 3 years and I definitely know what I'm doing. I was just asking about a timer circuit not your condescending, pointless rant. thanks anyways :)

The timer is only the first step in the procedure, these tools have been ran for years and have a very good safety rating. First the timer hits 0, then the signal travels to a pressure switch, if the correct pressure threshold isn't met the voltage stops right there and no kaboom. Lastly it travels to a temperature switch and if the set temperature is not reached then the circuit remains open and no fire on the end of the tool. It takes 1 amp of current to set off the electric detonator. I've been doing this type of work for 3 years and was only asking about a timer circuit, I think an oscillating timer will work fine. All of these components would be protected and sealed in steel housings and tool's outside diameter is roughly 1.687". They are hoisted down the hole with stainless steel line that is normally .108"

CR4 Admins - PLEASE close this thread.

Most any discussion dealing with explosives - and in this case one being asked by someone who clearly doesn't seem to quite know what he's doing - should be highly discouraged. Obvious personal safety implications aside, we don't know the actual agenda of this individual.

Jwayne13, consult a local explosives expert. Don't trust your life or the lives of others to some advice posted on an internet forum!

I am the local explosives expert, I'm not asking how to set off a detonoation, I was simply asking a suggestion on a timer circuit. I've been doing this for 3 years and still have all my fingers and toes.

well, not wishing to burst your bubble, you don't seem like an expert if you have to ask questions like this. You don't see heart surgeons asking how to perform heart surgery on the internet. It is for this very reason that people in general have little respect for engineering.

use monostable timer ic 555

T=1.1RC

from the value of resistance and capacitor

4 the voltage its depend on the capacitance

thanks, I was just double checking my own research to see if anyone had a better suggestion.

How about a Twist style mechanical timer like in a simple kitchen egg timer.

I measured mine and it will fit in the container you described.

It still worked in the oven at 350 deg F. (metal parts)

The mechanical bell dinger could be replaced to make a physical connection between two power leads.