D. E. Stearns
MODEL M/1 WET SPONGE HOLIDAY DETECTOR
DESCRIPTION. The Model M/1 Holiday Detector is a highly sensitive device designed to locate holidays (pin holes, voids, etc.) in thin film protective coating of relatively high electrical resistance when such films are applied to the surface of material of low electrical resistance. In these applications, such as painted metal surfaces, the Model M/1 Holiday Detector will locate these points very accurately with an audible signal. This method of inspection of thin film is a non-destructive test and will not injure the protective coating.
EQUIPMENT. The Model M/1 Holiday Detector consists of a portable battery powered electronic instrument, a non-conductive handle w/ sponge clamps, open cell sponge (cellulose) and ground wire. The instrument is housed in a sturdy plastic case with provision for attachment to the operator's belt. The detector is a "non-destructive wet sponge" type holiday detector. The basic electronic design of the Model M/1 Holiday Detector is a very sensitive circuit, which is energized by six "AA" batteries. When current of 500 or 700 (+/- 10/%) microamperes flows in the circuit, an audible signal is actuated. The test lead wire used in the wand handle and ground wire is capable of handling a minimum of 100 milliamps at 100 volts. If replacement or additional wire is needed, make sure it meets these requirements. Length of ground wire does not adversely effect the detectors operation. The exploring electrode is open-cell sponge material and is conductive when saturated with a wetting solution. The sponge electrode is attached to the non-conductive wand handle by securing it between the metal clamps. The wetting solution should consist of potable tap water and a wetting agent. The ratio of one (1) ounce agent to one (1) gallon tap water is recommended. D. E. Stearns WATER-WETTER(c) is a non-sudsing wetting agent, available in 8 oz. bottles, factory direct or through stocking distributors.
RECOMMENDED TESTING PROCEDURES PRE-ELECTRICAL TEST PROCEDURES. The protective coatings should be dry and free of all contamination prior to electrical holiday testing. Proper curing and drying time of the protective coating must be established prior to conducting electrical holiday testing. Note: Solvents retained in the protective coating film can cause erroneous indications (false holidays) during electrical testing. The dry film thickness should not exceed 20 mils when electrical holiday testing is done with the low voltage Model M/1 Holiday Detector. Film thickness should be determined with a non-destructive dry film thickness gauge to make sure limits are not exceeded. Special Note: Ordinary tap water will generally suffice to dampen the sponge electrode, provided the protective coating thickness does not exceed 10 mils. The factory recommended practice is to use a wetting agent at all times, regardless of coating thickness to 20 mils. Check battery voltage. Shorting the terminals of the holiday detector can do this. If a steady, level audible signal is heard, the battery voltage is OK. If the audible signal starts to attenuate while testing, REPLACE batteries. Note: An output voltage drop of over 10% also indicates weak battery.
HOLIDAY DETECTOR ASSEMBLY. Assemble the Holiday Detector by connecting the wire leading from the handle to one terminal of the detector and the plain end of the ground wire to the other detector terminal. Connect the saturated (see below) electrode by means of the metal clamp on the end of wand handle.
ELECTRICAL TESTING PROCEDURES. The sponge electrode should contain sufficient amount of wetting solutions to assure moisture penetration from the sponge electrodes into any defect that may be present in the protective coating. Excess wetting solution should be squeezed out of the sponge electrode. Attach ground wire directly to the bare structure (substrate) under test. On coated steel structures the ground wire must be directly connected to the bare metal. On coated concrete structures the ground wire should be connected directly to the reinforcing steel embedded in the concrete. If re-bar is not present, a ground connection to the concrete can be made by placing the bare end of the ground wire against the bare concrete surface and anchor it down with a burlap bag filled with damp sand. The ground wire can be checked quickly for proper connection by contacting the wetted sponge electrode to the bare structure and observing an audible signal, indicating correct electrical continuity of the holiday detector circuit. The rate of inspection speed of the sponge electrode over the protective coated surface should not exceed sixty (60) linear feet per minute. Using a double stroke of the sponge electrode over each area assures better inspection coverage with less likelihood of any missed areas.
CALIBRATION. Factory calibration on Model M/1 Holiday Detectors are set at 700 microamperes (+ or - 10) of current flow to compete the circuit for the audible signal to indicate a coating holiday on metal substrates. For coatings on concrete substrates, the Model M/1 must be adjusted for current flow of 500 microamperes (+ or - 10%).
ADJUSTMENT OF SIGNAL SYSTEM.
Model M/1 Holiday Detectors with mechanical relays, the sensitivity may be changed by adjustment of the armature contacts. The signal sensitivity is determined by the setting of the electronic relay. Turning the adjusting screw of the potentiometer clockwise REDUCES the sensitivity and turning counterclockwise INCREASES the sensitivity. Factory setting of the sensitivity is made by having the relay just close when 80,000 ohms is across the external terminals which is the proper setting for use on coated metal substrates. For concrete substrates the sensitivity would be adjusted with a 90,000 - ohm resistor. Model M/1 Holiday Detectors, Serial Number 10181 and higher FACTORY calibration can be verified by simply depressing push buttons on the front of the instrument. Depress BLACK button (80K); Detector should signal and LED will light if detector is in calibration. Depress RED button (90K): Detector should NOT signal and LED will NOT light if detector is in calibration. If the detector signals when RED button (90K) is depressed, the unit is not in calibration and should be FACTORY calibrated prior to use. To check for proper calibration of the detector for use on concrete substrates simply verify unit is properly FACTORY calibrated at 80,000 ohms and then remove the small jumper wire inside the red cover side of the detector.
Warranty: 90 Days Parts & Labor with 24-hour turn-around on all repairs.
NOTE: When ordering parts, please include "Serial Number of Instrument"
D. E. Stearns
P.O. Box 3456
Shreveport, LA 71133-3456
Phone (318) 635-5351
Fax (318) 636-6969
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