Electrostatic Voltmeter
The Surface DC Voltmeter model SVM2 (Price $260 USD) is a handheld electrostatic voltmeter that measures essentially all the parameters associated with static electricity. Its principle function-- measuring the voltage of a sample or surface without touching it-- is intuitive and the meter can be used for this purpose immediately out of the box. In addition, it has features not found in any other handheld static meter, such as very high sensitivity. Its resolution is one volt at the standard measurement distance of 1" (2.5 cm), making the SVM2 the most sensitive noncontact voltmeter available (other than our Ultrastable Surface Voltmeter, which is 1/10 volt resolution at 1"). This additional sensitivity makes the meter practical for determining other parameters, such as a sample's "ohms per square" and discharge time, and a room's air ion balance. Static charge can even be measured on tiny submillimeter samples (correction formulas are required because of the geometry of small samples). The single range is + to -29,999 volts, in one volt steps, which means it can detect a small change even in a high voltage. There is also a user-settable alarm and a peak hold for both + and - voltage peaks, all with ultrafast 0.005 second response. Therefore, the meter can be used to scan large areas quickly for static sources. It will beep if exposed longer than 5 millisec to a voltage (whether + or - polarity) that is higher than the alarm level, which is settable from 10 to 20,000 volts in 300 levels (it can also be muted). Then by pressing the "- Peak Hold" or "+ Peak Hold" button, the meter displays respectively the most negative and most positive voltages that were detected since the last time that the "Reset" button was pressed. The peak hold function can also be used to measure AC voltage (approximately 1/3 the peak-to-peak voltage). These innovations have been incorporated so that the operator can effectively "see" static electricity with greater clarity and speed than has been possible before.
Additional information and specs follow. Contact us (see below) with any questions or to place an order. To order online, click here.
Thus due to its electronic design, the SVM2 is far faster than any other electrostatic voltmeter, but there are also mechanical improvements. The sensor is the metal disk shown on the back surface, and this backside location is not typical of electrostatic voltmeters. The typical sensor location for most meters is on the top, but a top location would require that the user turn the meter upside-down to measure a horizontal surface, such as a bench top. With the backside sensor location, the SVM2 can be held at a more convenient angle; while measuring any surface or object, the display will remain right-side up. The SVM2 also includes a detachable 1" spacer rod to standardize the measurement distance, when required. The rod is attached to a small magnet (center photo) which enables the spacer to adhere to the back surface. If it encounters an obstacle, the rod flips out of the way and then springs back into place. This design avoids damage but allows the operator to "feel" the correct spacing even at a rapid scan speed.
With this meter, all of the following can be measured:
-The amount of charge (or voltage) on surfaces and the effectiveness of antistatic processing. Measuring a tiny fractional change in the
surface voltage is useful because it tells you whether the problem is getting better or worse as a new remedy is tried and modified.
-The location, strength and polarity of all static sources. Because of the speed of this meter, unexpected sources are easily found.
-The number (per square cm per second) of air ions that are hitting a surface, and the effectiveness of ionizers and discharge devices.
-DC Electric field strength in air (also AC, which is 1/3 of the difference between + and - peak hold numbers).
-The approximate conductivity or ohms per square of surfaces.
-The approximate attractive/repulsive force between charged surfaces. (This can be calculated from the readings.)
-Voltage differential through the thickness of an insulating sheet or film.
Full details on how to perform these measurements are here.
This meter is not recommended for long-term automated measurements, such as connection to a data acquisition system. Note that an optional output jack can be ordered, but it is only useful for AC detection, and should be used with an external multimeter or oscilloscope. This meter should be manually reset at least every 20 minutes in case the sensor had acquired any charge, and at very strong ion levels (if a lot of sparking is present), external ions will add enough charge that the reset must be done more frequently. (For a stable electrostatic voltmeter which is chopper stabilized ["field mill"], so it can be used for long-term automated measurements without ever needing to be reset, click here.)
Typical Way the Meter is Used:
This type of meter is most often used to measure static charge on a surface or object. In order to eliminate a static electricity problem, the meter measures the amount of charge from one moment to the next as the object is processed or handled, so you will be able to identify which step in the process is introducing or removing the charge. To perform measurements, either connect the meter to earth ground with the supplied cord (connect to the plug with the raised black circle around it), or simply touch the meter at the nearby bare metal circle if you are already grounded. If you are not using the ground cord, but you are personally grounded, continue to hold your finger against this circle. Turn the meter on and perform a “Reset”. To “Reset”, hold the rear area of the meter (where the sensor disc is) near a grounded conductor that is large enough to cover most of the horizon (if you imagine that the sensor disc were an eye). This grounded conductor can be your hand, but if you use your hand, you must be grounded during the “Reset” step (touch the metal circle). When covering most of the horizon of the sensor disc, make sure that the ground is not actually touching the disc. Then press and release the "Reset". This process takes about three seconds, and it sets the meter so that “zero volts” is the same as ground (+/- a few volts). This step is usually only done once, at the beginning of a measurement session or every time you turn the meter off and back on. (However, the step may need to be performed more often in an ionizing environment.) Occasionally check that the reading remains near zero by covering most of the sensor disc with your hand (while touching the metal circle) without pressing "Reset"; if stray charge has gotten onto the disk, the display will not read zero. If this happens, repeat the "Reset" step.
To test an object, point the sensor disc toward the object, without actually touching it to the disc. (An included one-inch spacer rod will be magnetically held in place just below the sensor disc if it is brought near that position. The rod is used to standardize the distance between the disc and the object.) Hold the meter so your fingers don’t protrude past the rear face. This prevents your fingers from accidentally discharging the object or altering the reading. At a spacing of one inch, the meter will read the surface voltage of a conductive object, in kilovolts (kV). It also reads the voltage of an insulator, although voltage on an insulator acts differently from voltage on a conductor. (See "Interpreting readings..." below.) The reading is accurate +/-2% provided that the surface is at least 10 inches wide and the spacing is 1”. If less than 10 inches wide or at a different spacing, there are formulas that allow estimation the actual voltage of the surface. If the object is less than 10 inches wide, the display will read lower than the actual voltage (formulas below). The range is -29.999 to +29.999 kV (-29,999 to +29,999 volts). The increment, or resolution, is .001 kV (= 1 volt). If the voltage goes above 19.999 kV, an automatic safety alarm will sound until the voltage drops back below 20 kV.
To test a large area, begin as above, but scan the area (at approximately a constant distance-- The preferred distance is also 1” or 25 mm. The magnetic spacer rod can be used. If the rod hits an obstacle, it will tip and then spring back into place.) The alarm can be set if needed (i.e., if your application has a maximum tolerable voltage, or if you want to hear a tone wherever the static voltage is high). To set, Press "Alarm Set” and simultaneously press “+” or “-”. You can immediately set the alarm to zero, which mutes it, by pressing “Reset” while “Alarm Set” is pressed. Note that the alarm resets to zero when power is turned on. If the actual voltage exceeds the alarm setting, the alarm will sound unless the alarm is set at zero. This is true whether the actual voltage is positive or negative. The response is very fast, so you can immediately identify where the “hot” areas are. After scanning, you can press “- Peak Hold” to read the most negative voltage, or “+ Peak Hold” for the most positive. These are the peaks since the last time a "Reset” was done. The response time of these two peak holds is 0.005 seconds (which is much faster than the display update time). These numbers will stay in memory until a more negative (or positive) voltage appears, or until a “Reset” is done or ON/OFF is pressed.
Interpreting readings at other distances or from small sources: Unfortunately, there are some subtleties in the physics of electrostatics, and they are mentioned here in order to be technically accurate. For most purposes, you can skip these two paragraphs. If you are measuring the voltage of a metal object or sheet that has large dimensions (large means more than about 20x the diameter of the sensor, of 1"), then the voltage of that object is well-defined and it does not change much if you move the sensor closer or farther. The voltage is also well-defined on a small metal object if it is connected by wire to a large piece of metal or a constant voltage source. With this type of metal object, the voltage remains constant when a grounded sensor or a hand is brought closer because the surface charge on the object increases in exactly the right way to keep the voltage constant. This extra charge flows in from the other parts of the metal or through the wire. If the static source is an insulator (or an insulator that has small, isolated metal pieces on it), charge cannot flow in this way. Therefore, the surface charge on a given area will remain constant as a grounded sensor or hand is brought closer. In fact, if a grounded metal sheet is brought into contact with a charged insulator, the surface voltage will drop to zero even though all or most of the surface charge will remain on the insulator. (If the grounded sheet is then pulled away, the surface of the insulator will return to its previous voltage.) Therefore, a large metal surface (or a small metal connected by wire to a large one or to a voltage supply) will have a constant voltage but a changing surface charge as a grounded conductor is moved into proximity. An insulator is the opposite; voltage changes while surface charge remains constant.
Suppose the static source being measured is a large (more that 10 sq meters) metal sheet at voltage -1000 volts. At the standard spacing of L = 1", the meter will read "-1.000" kV, as expected. If the spacing is then increased to 10", the meter will read approximately "-0.333" kV. Therefore, at 10" from a large metal sheet, the displayed number must be multiplied by 3. Here are some values at other spacings: At 5", multiply by 2.2 - - At 2", multiply by 1.4 - - At 0.5", multiply by 0.67 - - At 0.25", multiply by 0.41 - - In contrast to metal, if the source is a large insulating sheet with uniform charge across the surface, the meter reading will not change with spacing, so multiply the display by "1" at any of those spacings. There is one more variable: the size (diameter) of the static source. Again, there can be a difference between a metal (conducting) and an insulating source. Call "L" the spacing, in inches, from the sensor disc to the static source (normally, L = 1"). Call "D" the diameter of the source that is being measured (you may have to approximate the value of D if the source is an irregular shape). If the source is either metal that is not connected to a voltage source or an insulator, just multiply the displayed number by (1 + 42/D2) and ignore the correction factors above. For example, if the source is a metal disc, sitting by itself (not connected to a wire that could hold it at a certain voltage), and this metal disc is 2" in diameter (D), and also you are measuring with the sensor at 5" (L) spacing away from the metal, if the display reads "0.200 kV", then multiply by (1+ 4x52/22) = 26 to get a true reading of 26 x 0.200 = 5.200 kV. (This "true reading" can be used to determine the amount of surface charge per area on the metal). The "true reading" would also be 5.200 kV if the display was reading "0.200 kV" with only a 2" diameter insulator present. On the other hand, if the source is metal that is connected to a wire, multiply the display by the listed value above (i.e., if L = 5", multiply by 2.2) and then multiply that by the square root of (1 + 4L2/D2). This will be the true voltage of the source. If the displayed voltage is "0.200 kV", then multiply that by 2.2 times the square root of 26, so the true voltage is 2.244 kV.
Specifications:
Surface DC Voltmeter Model SVM2 Specifications
Range: 0 to +/- 29.999 kV (@ 1". Resolution is 1 volt (0.001 kV). Higher voltages can be measured, but at greater distance to avoid sparking, and formulas are used to correct the readings.
Sensor type:Metal disc. The display reads a number proportional to total charge on the disc, which remains within 3 V of ground over the +/- 30kV (displayed) operating range. Capacitance is 3 nF, and for each 1 V on the disc, the display reads 10 kV, so that the sensitivity to accumulated charge is 10 kV per 3 nC (3 nano ampsec).
Drift and leakage: Sensor resistance > 20 T ohms, which results in a self-discharge half life > 10 hours in the absence of air ions. Maximum drift current on the sensor is +/- 5 fA (5x10-15 amp), which results in a maximum display drift of 1 volt/minute.
Accuracy: +/- 2% of reading (example: a reading of 1.003 kV is accurate to +/- 0.020 kV). This assumes that the meter was correctly "Reset" initially.
Battery: Standard replaceable 9 volt rectangular battery (included). Battery life is about 30 hours (12 milliamp drain). LOW BATTERY displays when about 2 hours are left.
Display speed: 4 updates per second. Full response to a sudden change is 1/4 second.
Reset: If pressed, this button simultaneously removes the accumulated charge on the sensor (which causes the display to read zero) and resets both the Peak Hold memories to zero. If "Alarm Set" is held down first and then "Reset" is pressed, the alarm threshold is reset to zero. In this case, the sensor charge and Peak Hold memories are not reset.
Alarm Set: Press this to display the present alarm threshold value. While holding this button, press "+" or "-" to change the value (0 to +20.000 kV), or press "Reset" to return to zero.
Standard Alarm Function: Between -20 kV and +20 kV, the alarm sounds if the actual voltage is above the "Alarm Set" number. If "Alarm Set" is zero, the standard alarm is disabled (muted).
High-Voltage Alarm Function: A safety feature--if the voltage ever exceeds 20 kV, sparking becomes likely. A different (lower) tone sounds even if the alarm is muted.
Sampling Speed: The Peak Hold and Alarm both sample continuously. The characteristic (1/e) time is 0.005 sec. Guaranteed 98% response for any a pulse that is 0.015 sec or longer.
Auto Off: If no buttons are pressed for 10 minutes, the meter will turn off.
Warranty: One year. A certificate is optional. Meter can be recalibrated by AlphaLab Inc. This meter does not drift in gain, so recalibration is not necessary in less than 10 years.
Includes: Meter, 20 foot grounding cord (necessary if user is not earth grounded), magnetically-attached 1" spacer, battery (already inserted). As shipped, the meter is ready to use.
Surface DC Voltmeter Model SVM2: $260 (US dollars). Shipped ready-to-use; standard replaceable 9 volt battery inside. Usually shipped within one business day, the meter manufactured by Alphalab, Inc. in Salt Lake City (USA). Warranty is one year.
Hard case: $12
Calibration Certificate: $30
Output Jack : $15 (1/8", with plug; analog signal, 2V out = 20 kV actual voltage.)
Shipping to US: Free (UPS ground from Salt Lake City or Priority Mail, if requested. Other options are available.)
Shipping to Canada): $20 (GST must be paid when delivered.)
Shipping to all other areas: $40 (VAT, GST or import tax is not included.)
For information or to place an order :
Toll free (USA and Canada) 1-800-658-7030
Telephone +1-801-487-9492
Fax +1-801-487-3877
E-mail mail@trifield.com
To place an online secure order, go to DetectorTechnologies.com
Both TriField.com and DetectorTechnologies.com are owned by
AlphaLab, Inc. / 3005 South 300
West / Salt Lake City UT 84115 USA