High Temperature Electronics
High temperature electronics is used in a variety of environments from automobiles to oil well equipment.
A key factor in designing and choosing high temperature electronics is whether the electronics will be in high temperature for a limited time or for extended time.
If the electronics package is in high temperature for a limited time, the electronics can be pre cooled and insulated. Aerosol gel or aerogel is one of the best insulators known. Dewar flasks can be used for even better insulations.
In addition the electronics can be packed together with a cooling pack, to extend the time it stays cool. This is like placing the drinks in ice to keep them cool.
If extended operation is required the electronics package can be cooled using active cooling, or be designed to operate at high temperatures.
Active cooling may involve cooling components or cooling the whole assembly. Peltier cooling is an example of active cooling This consumes power.
Alternatively electronics can be designed using discrete components that work at very high temperatures. This is limiting because in practice only a limited amount of intelligence can be built into controls using discrete logic. Also discrete components that are qualified to work at high temperatures are expensive. Honeywell makes discrete components that are qualified to work at high temperatures.
Temperature rise occurs because of heat coming in from outside the electronics and heat being generated by the electronic components themselves. Hence it pays to keep the electronics design as low power as possible.
Recent Developments - Cheap, Commercial High Temperature Electronics
These are mostly a spin off from the automotive electronics market.
Examples
- PIC12F615 is rated at 150C, is in stock for next day delivery and costs about $1
- Advanced dspic33 processors are rated till 140C, cost from $7 to $10, are available for next day delivery
The availability of these electronics means that
- No special measures have to be taken at not so high temperature wells
- Cooling and insulation requirements are reduced at high temperature wells
- Intelligence can be embedded in the module.
Communication chips that work at high temperatures are also now available. Texas Instruments CC1101Q1 RF transceiver chips that work till 125c.
These might obviate the need for wireline communications for oilwell electronics if a battery pack is included with the electronics pack and RF safe perforating explosives are used.
High Temperature Electronics - Temperature Categories
Electronics can be categorized by temperature as follows
- Upto 150C - no problem, no special cooling required, commercial relatively cheap components available
- 150 - 175C - possible without special cooling, components have to be especially qualified
- Above 175C - electronics should be placed in insulated containers. For long term operation active cooling maybe required.
Results from testing our High Temperature Electronics Designs
We have run tests using Aspen Aerogel fabric as an insulating material.
We filled a small cylinder with water and ice, insulated it with the Aerogel fabric and placed it in an oven maintained at 400F/204C. After two hours, the temperature of the water inside the cylinder was 200F/95C. While there is still water in the container, the temperature is held steady at around 100C/212F inside the chamber.
The construction was simple and achieved its goal. We can achieve even better results at higher costs if we minimize radiation by coating the inside of the cylinder with reflective material.
For example, when we ran a similar experiment using a Dewar flask, the temperature stayed below 100C even 10 hours after being placed in an oven maintained at 400F