Examination of a Vegatest Device
Robert Mosenkis, PE, CCE
This report summarizes the findings of our examination of a Vegatest I instrument that bore Serial No. 701274 and a date of 08/87 handwritten in a blank (labeled Datum) on its nameplate. In September 1997, we opened the unit and its probe and examined them, and then conducted some operational tests.
The Vegatest 1 operates from wall power. It is housed in a green plastic cabinet with a metal front/top panel. All legends are in German. Toward the front of the top surface is a heavy aluminum-like block of metal (described in Apex Energetics literature as a honeycomb) that contains a number of holes, or wells; they do not penetrate the bottom of the block. Glass ampules may be placed into the wells in the honeycomb; we were provided with one such ampule, labeled Clostridium tertium.
Above the honeycomb is a panel of eight interconnected push-button switches; pressing any one of them releases any other switch that had been depressed. The leftmost button is labeled Widerst, and the remaining ones are numbered I through 7. On the very front panel are six banana jacks with two-letter labels that, we were told, correspond to various pans of the body (e.g,, scalp) to which electrodes could be connected. During our examination of the interior of the unit, we determined that the seven switches are connected to these jacks. There is also a multipin connector on this front panel, by which the cables from the two probes connect to the instrument.
There, is a control knob to the right of the honeycomb that operates a switched potentiometer. Above it are two LEDs in a box labeled Akku—a green one, marked Ladung, and a red one, marked entladen. A nearly vertical portion of the front/top panel contains a meter, graduated from 0 to 100; a switch, labeled Ein and Aus; and a red LED, labeled 0 ... 2,5 N (this could stand for newtons, a unit of force). Neither of the two red LEDs lit during any of our investigation.
During our initial experimentation, we found that the meter normally reads zero and there is no audible output. Holding the large, cylindrical probe (which we will call the reference probe) in one hand and pressing the tip of the smaller-diameter probe (which we will call the active probe) against portions of the opposite hand caused the meter to deflect and an audible tone to be beard from the back of the unit. The harder we pressed the active probe against the skin, the higher in pitch and volume the sound became and the higher the meter would deflect. This would occur only when the leftmost of the bank of eight buttons was pressed and the switch was in the Ein position. There was also a small push button on the active probe. Pressing it would cause the meter to deflect to full-scale or higher, regardless of any patient contact with the probe. To reach a consistent starting point in further testing, we always turned the knob to provide a meter reading of 100 with the probe button depressed. This occurred with the knob fully counterclockwise, or in the "click" position beyond that setting; any clockwise rotation of the knob with the active probe button depressed would cause off-scale meter deflection
We opened the Vegatest I and found it to be a rather complex printed circuit board that included, among other high-quality components, four microcircuits ("CMPS"), four trimmer potentiometers with sealant to keep their setting, a power supply, and a rechargeable 9 V battery, The device was very well constructed. None of the conductors or wires were shielded, a sign that there were no high frequencies in the circuit. The printed circuit board appeared to have provision for additional components; perhaps these are used on other models. This is not unusual. The back of the honeycomb was, as expected, just solid metal. Unshielded wires are attached to two points on the.block. One connection point has two wires: one goes to the circuit board, the other one goes to a green banana jack on the side panel of the instrument.
The active probe is the size of a thick fountain pen. It has a metal barrel and a gray plastic tip with a small ball electrode protruding from the front, We unscrewed the tip, and the ball electrode came off with it (it was a press fit onto the internal portion of the electrode). We then opened the active probe; it contained two narrow printed circuit boards separated by a microswitch at one end and a small brass block at the other. As with the instrument itself, these circuit boards had provision for additional components or wires, not used in this model. The ball electrode press fits onto an internal brass part, which is approximately the size and shape of a ballpoint pen refll. A compression spring on the back of this part seems to keep the probe retracted. We were puzzled by this spring, because there would be no way that the probe would ever be extended in normal use; it could have something to do with making electrical contact to this brass part.
We had no operating instructions for the Vegatest I; only some promotional literature from Apex Energetics. With the case open, we made a number of measurements. First, with the unit unplugged, we measured the voltage across the rechargeable battery; the 9 V battery read 1.5 V, suggesting that it was no longer holding a charge. We then plugged the unit into line power (it has no on/off switch), and the battery voltage rose to 16.5 V. We could not determine the purpose of the battery. We tapped into the two probes—active and passive—and connected them to a voltmeter. With no patient contact, we measured 1.6 VDC and roughly 30 mV at 60 Hz (the latter, being much smaller than the DC voltage, was most likely stray interference pickup, and we ignored the AC voltage). Pressing the button on the active probe, which caused a meter reading of 100, resulted in the probe voltage dropping to zero; shorting the two probes together yielded the same results.
We connected a resistance decade box across the probe and found that 150 kilohms caused the meter to read 50 (half of full-scale), and the DC voltage across the probe to drop to 0.8 V (i.e., in half). Thus, the source impedance of the instrument, as seen from the probes, is about 150 kilohms. Higher resistance values caused the meter reading (and the pitch and volume of the audio output) to fall, while lower ones resulted in higher meter readings and audio tones. The instrument reading and audio output were directly related to the resistance value connected across the probes. We were not surprised to find that moving the.glass ampule to various wells in the honeycomb had no effect on the readings.
We then attached the active probe to a force gauge, so that we could press it against the hand with a known force as we held the passive probe in the other hand (tightness of that grip, beyond a small minimum value, had no effect). We found that pressing the probe tip against various parts of the hand had different effects. Some places required force of 1 kg or more to get significant readings, while other places (especially the web between fingers, which tends to be more moist) gave the same readings at 200 to 300 grams of force. Pressing the probe with a constant force resulted in a reading that drifted somewhat lower over a period of 10 to 15 seconds. Pressing the probe against a gold wedding ring (which had a larger contact area with the finger) resulted in a higher, more steady meter reading of about 45. Pouring a small quantity of normal saline on the hands and allowing it to partially dry resulted in higher readings for a given pressure.
Moving the glass ampule to various wells in the honeycomb had no effect on readings with the probe against parts of the hand (the person manipulating the vial was not the same one that held the active probe). This is consistent with our expectations, given that the honeycomb was made from a solid block of metal, especially since the ampule was made of glass, an electrically nonconducting material.
We connected the resistance decade box across the probe again and found that 500 kilohms yielded a meter reading of 22 and a DC voltage of 1.26 V. We removed the resistor box and pressed the active probe against a subject's hand sufficiently hard to yield a meter reading of 22. The DC voltage was 1.26 V, the same as with the resistance box.
Although we are somewhat at a loss to explain its complex circuitry, and "reverse engineering," the circuitry was beyond our scope, the investigations described above suggest that the Vegatest I is simply a resistance-measuring instrument (perhaps a very accurate one). We did not investigate the use of the panel of banana jacks, which are supposedly intended for connection of other electrodes.
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Mr. Mosenkis is president of CITECH, one of about a dozen companies that are accredited to evaluate new medical device applications submitted to the FDA. He served for many years as editor of Health Devices, a magazine similar to Consumer Reports but written for large purchasers of medical devices.
This article was posted on September 11, 2001.