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  1. logbook

    Is there a rule of thumb to follow when choosing a calibrator?

    TUR (Test Uncertainty Ratio) in modern terminology. If you use a TUR of 10:1 you tend to ignore the uncertainty in the calibrator completely. At 4:1 you may then want to consider "guard banding". there are some excellent articles on the web on this subject. Google "TUR" and "guard band".
  2. logbook

    ABET

    "Lab work" is really important hands-on experience. A professional course is not credible without it.
  3. logbook

    Posting whitepapers

    There are five on my publications page ... http://www.logbook.freeserve.co.uk/publications.html
  4. logbook

    Non Linear Load Bank Design

    Well a FAST rectifier and a decent capacitor will produce an arbitrarily high crest factor load. However will your source support such a crest factor? the trouble with teh mains as a source is that standard mains is harmonically distorted. Look at the waveform and the sinusoid is flat topped...
  5. logbook

    Noob multimeter question

    >On their website the accuracy is listed as: >Accuracy ± (0.05%+2) >The 2 means 2 LSD, so is it accurate to 0.1 ohm then since the range is listed as 500.00? The accuracy depends on the reading. Let's work through it. Suppose you are measuring roughly 500 ohms. 0.05% of the reading is 0.25...
  6. logbook

    Safe rechargeable battery lasting an entire week?

    Let's play with some numbers. Say a 60W laptop. (Not sure how reasonable that is) Say 5 hours per day (lazy days!) say 5 days per week. That's 60 (watts) * 5 (hours)* 5 (days) = 1500 Watt.hours assuming no maths errors. Let's take a lead acid at 13V. At 1A it delivers 13W. For 1500 Watt.hours...
  7. logbook

    high current JFETs

    Of course we are going back to basics here, but charging a capacitor from any resistive device dumps 0.5*C*V*V into the resistor. Sounds like you are charging to 15V which means 2.2kJ in the resistor. Have you considered using a power inductor to charge the capacitor. This will improve the...
  8. logbook

    Research Papers/Knowledge

    See if this fits the bill http://www.logbook.freeserve.co.uk/seekrets/index.html There are also many key papers listed, as compared to listing hundreds of less important related papers.
  9. logbook

    Finding Case Temp

    Case temperature is the thing you measure with thermocouples. Die temperature, the temperature of the chip, is calculated from the case temperature, the power dissipated in the chip and the thermal resistance from chip (junction) to case.
  10. logbook

    RTD

    If you measure across the terminals and it is around 100 ohms (when dunked in ice water; around 108 ohms at room temperature) then it is a fair bet that it is a 100 ohm platinum resistance thermometer. If it is 10k it is some sort of thermistor.
  11. logbook

    Battery Charger 12 volt

    Depends what you mean by a PLC. If you use an ADC with an SPI interface, would your PLC have enough gates to handle it? This is perhaps more FPGA territory, but perhaps that is covered by your term "PLC". The gauge could be done in firmware (VHDL) or software, depending on your overall system...
  12. logbook

    DMM Accuracy Spec- How to Interpret?

    Yes. Top marks on your results. This maths looks a bit dodgy though ... 12.60V x .8% =.10 (12.6-.10) = 12.50 Looks like a cut and paste error. I would have gone 12.60 + 0.8% = 12.6*(1.008) = 12.70 12.60 - 0.8% = 12.6*(0.992) = 12.50
  13. logbook

    DMM Accuracy Spec- How to Interpret?

    The % of reading is a gain error. The % of FS (or just a number of digits) is the linearity error. In modern terminology I should be saying "uncertainty" rather than "error" You are nearly there with your 10V example. The meter might read 10.00V. ±0.8% is ±8 digits and then you have another ±5...
  14. logbook

    Battery Charger 12 volt

    >The question is I need to have a "Fuel Gage" and/or a charger than can talk to the plc. Strictly speaking that is not a question. If you could spend a few minutes writing down what you need then you may get some appropriate help. For example you would like to run the unit on 6 gel cel...
  15. logbook

    splitting the mains

    zapped, no I meant directly soldering to the faston spade that comes out of the IEC inlet. Sometimes they have a hole in them to poke wires through which makes it easier. The only problem is possibly over-heating the faston when soldering. I wouldn't put two wires into a faston crimp...
  16. logbook

    two 24VAC Sources to one 5VDC

    >I used a dual primary 115V/230 transformer. Instead of hooking the primaries as usual, I hooked one Hot to the top of the transformer and one to the bottom and used the two in the middle as the neutral. Sounded good at first ... but one primary will strongly couple to the other. The ON circuit...
  17. logbook

    two 24VAC Sources to one 5VDC

    The key to this problem relates to just how much power you need at 5V. If it is quite a lot then you will want to use some transformers to step the 24V AC down to 5V DC. The efficiency of the proposed schemes is so low that for every watt of 5V power you use, you are dissipating 5 watts. You...
  18. logbook

    splitting the mains

    I share your concern. The issue is not so much reliability but safety ... in terms of meeting the relevant regulations. Piggy backing the mains terminals with fastons is not ideal either. How about hard-wiring the end at the mains inlet, ie soldering two wires to each terminal. They would of...
  19. logbook

    Looking for help/info on photo diode project

    3 foot at 0.25 inch pitch = 3x12x4= 144 sensor pairs and you need two. What you are proposing as a "cheap system" requires 288 sensors and a >300 pin FPGA to do the digits. That is not cheap! This means MUXing to reduce the pin count. So the $1000 question is what do you mean by "quite fast"...
  20. logbook

    Static problem with plotter

    It would be a good idea to make sure the vinyl roll is earthed/grounded. As the vinyl is unwrapped it will create a static charge and this needs to be dissipated. Tinsel or specialist static control brushes should lightly touch the outer surface of the roll, ideally on the freshly exposed inner...

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