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14. Mär 2016
Super Durable Printer
The SP200 are single color (purple or black) or two color (black/red) printers with built-in Verifone 200 emulation which are ideal for credit authorization terminals (CAT) and data logging systems. The optional CAT cover provides an ergonomic receipt printer and CAT package. Standard features include small footprint, Parallel or Serial interfaces, semi-automatic paper loading and MCBF/reliability of 9 million lines. The integrated cash drawer driver helps maintain minimum system cost. The built-in self test function allows the user to check and reset dip switch settings. The printer utilizes popular 3 inch wide roll paper and can print an original plus two copies. The long life metal tear bar or optional auto-cutter provide accurate and reliable paper cutting.
The Star SP200 is also known as the Star Micronics SP200
30. Jun 2016
FLUKE 893A AC/DC Differential Voltmeter 'AS IS'
This instrument is entirely solid state (transistors) but it's still pretty old. I have a manual for it that is dated 1969. So it's probably around 40 years old.
This is an analog voltage bridge, not a digital output voltmeter. You attach your input leads to the voltage to be measured, then adjust the scale and bridge voltage knobs to yield a zero on the nulling meter (an analog electromechanical meter). It's been a while since I knew much about this meter but, if I recall correctly, it uses a specialized and very stable zener diode as its voltage standard. It can also measure AC voltages, but I haven't looked into how it does this (I suspect it uses an "ideal" rectifier circuit and then compares the rectified AC to its DC zener standard voltage... but I don't really know!). Note that the electromechanical nulling meter will tend to average out AC ripple (the needle can't move instantaneously).
Below is a picture of it measuring the voltage output of a new 9v battery. I've also got the battery connected to my Philips PM 2534 digital meter for comparison.
The nulling meter position tends to wander a little. But I did my best to get it to about the zero point. Note: since this meter is so old, the nulling meter's zero point (the point it goes to when the meter is unpowered) is just a tiny bit away from the zero reading on the meter (it's just a bit to the left of the labeled zero). There's no obvious front panel mechanical screw adjustment to re-center the meter - but I haven't opened the case. So when measuring this battery, I just adjusted the nulling meter so that it sat at the same point it does when the meter is unpowered... just a tiny bit to the left of zero on the scale.
NOTE: Since writing this page I received a very generous email from a reader "W5JG" pointing out the following information:
"I saw your boatanchor blog entry for the 893A. There is a meter mechanical zero. It is hidden inside the slot for the Null Sens. You have to look hard to see it."
It's VERY hard to see in the picture below, but it's a slightly darker spot (a hole) on the lower middle of the black rectangular digital dial just below the analog meter and fuzzy words "NULL SENS". My thanks, W5JG.
The impressive thing is that this old instrument gave me a reading within a tenth of a percent of my more modern, high accuracy, Philips digital meter. See the picture below. The reading on the bridge is approximately 9.6825 volts. The reading on the Philips meter is 9.6867 volts.
You may think that this meter is entirely obsolescent. But maybe we should stop to think a bit more.
In the last few years I worked for a company that designed and built fluorescent ballasts. These often included switchmode boost PFC (power factor correction) circuits that created a (roughly) 500v DC voltage from the input 120v wall plug AC. In order to filter out the high voltage output ripple, large electrolytic capacitors were attached across the rectified DC node. But 500v electrolytic capacitors were not really practical (they either didn't exist or were so expensive that they could never be used). So our company used two lower voltage electrolytic capacitors in series to withstand the high 500v DC voltage. The "theory" was that the DC voltage would divide equally across the two capacitors so that neither of their maximum voltage ratings were exceeded. Personally, I found this argument questionable.
When I joined this company and heard of this practice, I immediately thought this might be a potential source of failure. Because I know that components can vary from device to device or from lot to lot, I wondered how it was determined that the two capacitors in series would always each end up with about half the total DC voltage (so that neither of their voltage ratings were exceeded). I was told that the two series capacitor voltages had been checked with a voltmeter.
This answer pretty much drove me crazy. I knew that you probably can't measure the DC voltage across one of two really high resistance components (such as capacitors) in series using a standard voltmeter. The voltmeter's own impedance (typically 10 Megohms) may be much lower than the capacitor's resistance. So a DC measurement using such a digital voltmeter might well be meaningless. This concept seemed to entirely escape the thinking of my colleagues (for a lot of years, it appears).
Instead, in order to accurately measure the DC voltage across each capacitor in the series combination, a VERY high input-impedance balanced bridge circuit should be used.
I actually made a crude one in the lab myself and measured the capacitors' voltage accurately. Somewhat to my surprise, the voltage actually did divide down to extremely close to half the total applied voltage (within a few volts!) for the few examples I measured.
There are a lot of possible explanations for this. For example, it could be that the two capacitors used in my t
11. Okt 2016
Great value for great price......
The Tissot V8 is a powerful engine for the wrist. The bold chronographs confidently take their positions on the Tissot product 'grid' with their dashboard-inspired counters and tachymeter bezels. The Tissot V8 models will appeal to wearers with a good dose of adrenalin in their lives and zero tolerance for missing out on the action.