Jämsä-Jukola

jukola2013_2

I ran the second stage (13 km) of the Jukola relay in Jämsä on Sunday.

Clear skies and a more northerly location meant there was much more light during the whole night. Not nearly as pitch-black as I remember in Vantaa last year.

Since there are about 1600 teams competing there will be tracks from 2000 or more runners in the forest when starting the 2nd-stage from about mid-way or worse down the field. This means it's really more trail-running than independent orienteering 🙂 There are tracks to and from each control - you just have to pick the right track among many.

pt100 frontend - v2

Here is version two of a precision pt100 frontend for temperature measurements between +22C and +42C. The circuit uses a 4-wire connection with a +/-500uA sensing-current. It outputs a +/-10V voltage centered around +32C by way of a 112 Ohm reference resistor. The voltage over the reference-resistor can be used to correct for drift in the sensing-current.

Compared to v1 I changed the current source to the "Improved Howland" design, and assembled the instrumentation amplifiers from zero-drift op-amps with very small input offset voltage and input bias current.

Note: The op-amp shown, AD8551/8552/8554, is a single-supply +5V op-amp and this circuit will not work as such (NI Multisim will happily simulate it though!). Use e.g. OP2177 or OPA2188 for bipolar operation at +/-12 V.

pt100_piiri

Aluerastit, Länsimäki

An interesting course with controls #1-#9 in a very detailed area, then a few longer legs to #12 where the course criss-crossed over the swamp a few times before heading back south to the finish.

No major mistakes just minor ones: after #3 did not clearly identify the path, and took a wrong direction down the hill to find #4. Then on the #10-#11 leg I did not want to cross the deep "trenches" on these cliffs, so I back-tracked to avoid the trench (dark brown line on the map).

2013_06_12_lansimaki_qr

pt100 frontend

Here's a sketch for a pt100/RTD frontend circuit.

pt100_frontend_2013june11

There are a couple of ideas here which should improve precision:

  • 4-wire connection, to eliminate lead-resistance effects
  • Ratiometric measurement (both a reference and the signal go to the ADC). This should minimize effects from fluctuations in the sensing current.
  • AC-excitation. The sensing current can be reversed with at TTL logic signal. Some ADC chips have an output for this, and they average the measurement done with current flowing in both directions. This eliminates effects from DC-offsets (thermovoltages etc).
  • The circuit is centered around a particular temperature (here +32C) and the signals amplified so a twenty degree span of +22C to +42C should give about +/- 4 V output.

NI Multisim file for this: pt100_sensor_circuit_v3

Friday biking

A loop to Espoo and back. 47 km in about 2 hours.

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Itärastit, Latokartano

2013_05_25_latokartano_qr_splits

Nice going on 1-4, then a little slower to #5.
Towards #6 I first had the wrong direction and found the road close to #7 instead. Then again the wrong direction from the road towards #6??
7-9 OKish. Big problems on #10 - should learn to recognize these harder legs and play it very safe. Many paths that were not marked on the map lead to all kinds of confusion..

Firmaliiga 2013/2, Laakso

21.5.2013 Firmaliiga, Laakso
#6 the organizers had placed this control incorrectly - more than half of the field did not find it.
#9 only major orienteering mistake here - looking for the control on the wrong hill for about 3 minutes before re-locating using the road.
#12 someone had stolen the control flag! By itself the small EMIT-control taped to a tree was hard to find.
#13 should have approached control from above, not below.

Firmaliiga result 35./58

2013_05_21_firmaliiga_laakso