Diary


 * February 2:**

Present: Martin; Lukas

Started project. Set up this wiki.


 * Contact Details:**
 * <  ||< Phone Number ||< Skype ||
 * < Lukas ||< 0870578133 ||< gumis.ie ||
 * < Martin ||< 0872714277 ||< djmidnight ||
 * < Gavin ||< 0879926777 ||<  ||

Temperature Wind speed Humidity Rainfall Light levels Atmospheric pressure
 * List of possible measurements:**

Lukas researched max and min temperature values on []


 * Tasks:** Research pros and cons of building sensors for the following:
 * Martin:** Temperature & wind speed
 * Lukas**: Rainfall & light levels
 * Gavin:** Atmospheric pressure & humidity

1. Decide on the four basic measurements 2. Look at best type of sensors required. 3. Decide on signal type (4 - 20 mA, 0 - 10V) 4. Research circuit designs = =


 * February 9**

Present: Martin, Lukas, Gavin

Temperature Humidity Rainfall Light levels
 * 1. Decision on measurements to be made:**

2. **Decision on sensor types:** Temperature - PT100? Humidity - MPX4115A? Rainfall - ? Light levels - LDR


 * Shortterm Project Objectives:**


 * Lukas:** Design and protype the sensor circuit (PT100)
 * Martin:** Investigate and test analogue capability of FX1n; investigate software and programming issues. (Overall project)
 * Gavin:** Investigate methods and circuits for measuring rainfall


 * Useful site:** www.discovercircuits.com


 * Note**: Likelyhood that all signals to system will be 0 to 10V (to be confirmed)

All check in here Friday morning for status update.

Present Martin,Lukas,gavin
 * February 16**

We made up a wheatstone bridge using LT spice using different values.We set the PT100 to room temperature at 20 degrese which equals 120 ohms.The ouput voltage that the wheatstone bridge give out .17volts. The values of resistors are R1 = 11k R2 = 12k R3 = 100K R4 = 12k R5 = 3k

We then proceeded to construct the circuit on a breadboard we got similiar results but found that the voltage is to low for any accuracy on the plc.The ideal voltage we need for plc is between 0 - 10 volts to give us enough swing because the temperature range were looking for is between -14 and +30.

Present Martin, Lukas, Gavin
 * February 23**

Presentation done tonight - lot more preparation required for next deadline.

Lukas experiementing with designs for second stage amplifier for temperature sensor. Mapping of outputs for a variety of temperatures is required to confirm linear signal.

Gavin and James are investigating the possibility of using the circuitry of a electronic weighing scales to act as part of the rainfall sensor. This scales uses a strain guage as it's sensor. The challenge is to calibrate this for our own uses.

I am primarily keeping this wiki up to date and also looking at possible humidity sensors and circuits. I have put up some circuit designs on the humidity page.


 * March 1**

I found the circuit below in a book called: Fundamentals of Industrial Instrumentation and Process Control by William C. Dunn.

I will try to find values for the resistors.


 * March 2**

Built the instrumentation amplifier above. For R1 to R5 I used 47k resistors, Ra and R6 were 47k pre-set pots. For the purposes of testing, the bridge consisted of three 10k resistors and a LDR. Initially a +/- 15V supply was used to power the amplifier circuit and a +15V for the bridge. At first, I tested the circuit with the bridge disconnected and measured an output of 4.6V. I was able to bring this down to almost zero volts by adjusting R6 (offset adjustment).



The next step was to apply a frequency of 1kHz to the amplifier circuit and monitor the gain with an oscilloscope. A gain of approximately 5 was observed. By adjusting Ra, this gain could be reduced to almost unity.



Given the effectiveness of this circuit, it is possible that it could be used as the basis of all of the instruments. It would only be necessary to change the gain adjustment resistor to give the correct gain for each instrument. I also discovered that this circuit can be purchased as a single package. The INA 126 and AD630 are examples of purpose built instrumentation amplifiers.


 * Note on Book: Principles of Measurement Systems, John P. Bentley ISBN: 0-582-23779-3**


 * March 22**

Looking at fine tuning the wheatstone bridge. Developing an Excel sheet to do the relevant calculations - watch this space for results (here's hoping).


 * March 23**

Was probably a little over ambitious with my aspirations for the spreadsheet. However, it does allow me to experiment with various resistance values and plot the results. It seems to be successfully calculating the output voltage of the bridge for a variety of values at the "sensor" position.


 * [[file:Wheatstone V1.0.xls]]

April 1**

Plotted values of resistance against light using an LDR and Lux meter. The results were, as expected, totally non-linear. Not looking promising if we persist with the idea of giving a readout of the light levels in Lux over a 24 hour period.


 * April 13**

General work ongoing on various instruments. Details on instrument page.


 * April 20**

Working on the PLC code for taking in the signals from the instruments. The basics of this are in place. Hopefully, with calibration information for the individual instruments, outputting real quantities from the PLC should be possible. Sharp learning curve upcoming about the maths functions of the PLC!!!!

The code so far: