Jonathan's Carriacou diary: Feel the heat

Day 1

The Ice Men and Woman

Today was 'first day back at school' feeling. By that I mean it started off great and excited that turned into a slight panic by lunchtime, into the blues by afternoon and into an exciting challenge by late afternoon!

Our overall challenge as a group was to try and make ICE! We each had challenges to do to get to this stage. Kathy and I were to make thermometers, and we were happy to help each other on two different types. I chose an electrical device as I thought it might be useful to be able to remotely measure the temperature. Kathy went for a glass liquid version.

My midday blues were due to the meter that I was trying to make for the thermometer challenge not shaping up the way I had hoped. I think if it was something I was doing at home I would have cracked on with it enough to know what I should be doing but with the camera crews going around and wanting to film various stages of the process, I found it stopped me making the needed development steps.

Also everyone else seemed to be getting straight on with their challenges and I felt a bit worried. During lunch, I had time to think through what I needed to do and so I got stuck into a MK II design for the meter immediately afterwards. This worked really well and so I began to feel much happier about the challenge. Kathy and I made up two coils (1500 turns and 5000 turns) for the meter to try and boost its sensitivity. The meter kicked over wonderfully on the car battery.

I am hoping that tomorrow all of us will have time to brainstorm the ice-making problem.

Overall I feel just the right amount of uncertainty to make the challenge genuinely interesting (scientifically and technically) but not so out-on-a-limb to feel it is uncomfortably impossible.

Day 2

Today starts early and it's already hot! Up at 5.30, wash, do some meditation and then breakfast. Walk with Kathy to the lime factory. Talk to Kathy about how she feels things are going. We all seem to be full of energy and excited about things. Also talk about calibration points for the thermometers. She suggests using body temperature as well as boiling water etc.

Set up the bridge thermometer for its first, and on-film, testing which goes really well. It's so nice when a back-of-the-envelope calculation (done to the nearest order of magnitude in your head) actually works out in real life - in front of your eyes! It gave the sort of kick on the meter it should have done!

The 'in-my-head', 'back-of-the-envelope', type calculation about the meter thermometer:
I guessed, or could remember, that the resistance of the copper wire we have used for the thermometer should change by about 20 to 30% between 0° and 100°C. As each resistor is part of the balanced circuit, each will have half of the car battery voltage across it - that's about 6V. So a 20% change in 6V is about 1V. In other words, if only one of the bridge resistors is used as a thermometer, its voltage will change by about this much with respect to the other part of the bridge. I tested the meter I made on a 1.5V battery (from a camera) and it moved about 1cm. When I put the thermometer into hot water the meter moved about 1cm!! That's a really nice feeling.

If we are to make ice in this hot and humid place it occurred to me that we will need a lot of insulation. As a result it might be very difficult to get a standard thermometer into the right place and be able to read it. So I thought that an electronic thermometer would be best as you could have the active circuit fitted near to the ice-making part of the apparatus but also have thin wires to take the signals out to a remote meter where the temperature measurement can actually be done. That was the basis of the electronic thermometer design.

The design consists of four resistors each made from about 40m of very thin (~0.1mm diameter) copper wire. The electrical resistance of wire changes with temperature. It is this change in resistance that causes changes in voltage, which we can measure, and allows us to use the device to measure temperature.

Making the resistors

The coils were wound around a nail for neatness but the coiling was also done in a special way. Firstly, the wire for each resistor is measured out. Then the wire is folded in half so that the two ends are side by side and only then is the wire wound onto the nail. This was done for each resistor. This curious way of winding the coils produces a resistor with no inductance. Inductance is caused by a current flowing in the coil producing a magnetic field but in this case the magnetism is cancelled by the fold in the wire. This greatly speeds up the response of the circuit, when it is turned on and off and when the temperature changes.

The four resistors are wired in what is called a balanced circuit or sometimes a bridge circuit. The balanced circuit consists of two pairs of resistors wired in series (one after the other) across the battery. The meter is wired between the two mid-points of the pairs of resistors.

The thermometer works like this. If each of the four resistors are at the same temperature there will be exactly the same voltage across each. There is therefore no difference in voltage between the two metering points and the meter will not read anything - the circuit is balanced. If, however, we take one of the resistors and place it somewhere at a different temperature, its resistance will change, and so its voltage across it will also change unbalancing the circuit. A voltage difference now exists between the metering points and the meter reads the temperature change.

Back to the diary

The next step was to calibrate the meter. I asked Ellen for some coconut oil to immerse the coil into and this then can be put in boiling water. The oil protects the coil windings from oxidation etc. However, there were problems with the oil and Ellen slaved over the stove for hours to get me some good oil for this test.

Didn't have time to do the final calibration today but we did have time to show that the meter reads one way for cooling and the other for heating (with respect to air temperature) so I marked + and - on the meter to show heating or cooling.

The day ends with the first test run for the ice machine. This was a very exciting time but for some reason we could not cool enough to measure on the meter.

One Funny Moment

Mike L, Mike B and I were being filmed discussing the design of the insulated box for the experiment. Mike B draws the design on the wall while Mike L and I look on and contribute. While this was happening I looked over to Mike L and saw him smiling. At that instant Derek stands on my foot and I can't move and can't get near to the drawing to contribute. I find out later that at the same time I looked over to see Mike smiling, Derek was on his foot too! So neither of us could move.

Day 3

The Balanced Circuit

The balanced circuit is the one,
That makes our modern world run,
In TVs, radios and all manner of things,
This circuit even makes the telephones ring,
It's remarkable in this space computer age,
That the balanced circuit is still all the rage!

A Very Funny Moment

Kathy finished her thermometer today and Ellen and I helped to seal it. The filling with alcohol, sealing and setting up of the thermometer could only be filmed once as it was really, really tricky and time was running out. So the director, Sarah, shouted out to the whole factory: "Quiet, please, this can only be done once." All goes quiet and we start to film the sequence. At the crucial moment when all is calm and we are all concentrating on the problem, a donkey walks past the walls of the factory and in a very loud way starts to eeeeeeooooorrrrrr - look out for this one and the strained straight faces in the TV programme.

Calibration

Kathy and I calibrated our thermometers. Hers was sensitive, mine wider ranging. We both showed two of the many possible ways of making temperature measurements and both got the results we wanted.

Mike L's Doom Comment #9
In the middle of a tense moment of the shoot - "I'll never be able to clean this T-shirt with travel wash" !

A Mike B Funny
Mike B does a rather disturbing but incredibly funny impersonation of a drunk with the rum bottle Kate gave him. The ruffled hair, dirty T-shirt and the great acting was perfect!

I loved it, I enjoyed it, it was true to life, it was believable - it didn't work!! We didn't make ice. We did, however, make a great team effort in a very hot ambient temperature and humidity.

The last hours of the day were brilliant - pure magic. That wonderful mixture of a group focused on a common goal and the wonders of the unknown. Moments like that should be savoured but you tend to be so much a part of it that time goes and you are too soon left with memories to look back on. The programme was amazing in its Science coverage. I hope people understand the difficulty of the challenge and see what was really achieved.