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 The Model M1/AC 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 M1/AC 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. 


 The electrical components are housed in a thermo plastic resin case with closing lid for maximum protection and the detector is equipped with on-off switch, LED light, wand terminal, ground terminal, fuse receptacle, 110v AC cord. (For use with 240v AC, an appropriate cord will need to be sourced locally). The detector operates from 110/240 volt 50/60 cycle AC line current and the electrical design of the M1/AC Holiday Detector utilizes a sensitive relay which is activated by a voltage regulated, solid state power supply. 

The detector is a “non-destructive wet sponge” type holiday detector. The basic electronic design of the Model M1/AC Holiday Detector is that of a very sensitive circuit which is energized by AC power. When current of 500 or 700 (+/- 10/%) micro-amperes 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. Up to 200’ length of ground wire does not adversely affect the detectors operation, in most cases. If adding additional ground wire, 14 AWG stranded or equivalent is recommended. 

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 means of the bolt with knob, plastic sponge holder and backing plate. 

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 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. Tinker & Rasor WATER-WETTER© is a non-sudsing wetting agent, available in 8 oz. bottles, factory direct or through stocking distributors. 



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 M1/AC 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. 


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, located on the side of the instrument case. Connect the saturated (see below) electrode by means of the metal clamp on the end of wand handle. Plug the AC cord into a 110v AC outlet and turn the instrument ON. 


The sponge electrode should contain sufficient amount of wetting solution to assure moisture penetration from the sponge electrode 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 rebar 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. 


Factory calibration on Model M1/AC Holiday Detectors is set at 700 micro-amperes (+/- 10%) of current flow to complete the circuit for the audible signal to indicate a coating holiday on metal substrates. For coatings on concrete substrates, the Model M1/AC must be adjusted for current flow of 500 micro-amperes (+/- 10%). 


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 M1/AC Holiday Detectors are set with FACTORY calibration which can be verified by simply depressing push buttons on the panel 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 on the back of the printed circuit board, under the panel 

NOTE: The 80k ohm and 90k ohm internal resistors used for the internal calibration test stated above have an accuracy of +/- 1%. 


Holiday Detectors returned to the factory for repairs should be sent TRANSPORTATION PREPAID. In most cases the detector can be repaired and returned the same day it is received at the factory. 


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