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TROUBLESHOOTING HYBRID SURVEILLANCE SYSTEMS FOR Ground Loop Test Using a Camera Master DUMIES Video cable Meter should not exceed 0.1VAC TEST PROCEDURE NO. 2: USING A CAMERA MASTER If you are fortunate enough to have a Camera Master (CM-2) testing device by FM Systems, here is the ground loop testing procedure. To measure ground loop readings at the camera, switch the selector to "GROUND LOOP" and connect the ca- ble coming from the monitor equipment to either BNC connector on the CM-2. T en connect a short cable to the cam- era output. Take the lose end of the ca- ble and touch the outer shield (the metal outside portion) of the connector to the ¼-inch nut on the upper left-hand side of the meter next to the display. When the connection is made, a decimal point will appear on the display indicating a volts reading. T e reading will be the amount of ground loop voltage on the video cable. T is reading is calibrated in RMS and will indicate if you have a ground loop problem. To measure ground loop at the mon- itor end, use the same procedure ex- cept you connect to the DVR or monitor equipment instead of the cam- era. T e measurement is taken between the two cables using only the shield of each cable. It does not matter which ca- ble connects to the BNC con- nector and which cable con- nects to the ¼-inch nut on the side of the meter. T ey are in- terchangeable. Again, any voltage more than 0.1 or 100 millivolts, is the point at which prob- lems begin to show up on the monitor equipment. Video is 1V in amplitude and anything more than 10% interference will normally cre- ate a problem with the images.1 Once verifi ed, the next step is to insert a ground loop cor- rector or isolator. T is device will vary in cost between $125 and $200. T e device should be inserted in series with the ca- ble. It can be placed anywhere along the cable run. Some people may resort to shortcuts and try to remove the earth ground (the middle prong on a three-prong electri- cal plug) from the camera or the asso- ciated equipment. Not only is this very hazardous, it is also a violation of UL regulations. When the earth ground is removed, a voltage can appear on the camera chassis. T e camera will have what is called a "hot chassis" that can send a jolt of electricity through any- one who touches it, suffi cient enough to ARE NETWORKED CAMERAS BETTER GROUNDED? With the rapid rise of networked cameras, will there still be a need for ground loop correctors? Good question! There are two basic theories that would suggest that networked cameras should eliminate ground loops. The first theory is that the two center conductors of a balanced line act as the sole conduit for the signal. If any unwanted electrical interference enters these signal conductors, and because they have the same impedance to ground, it will interact with both center conductors equally. The effect in the receiving circuitry is that these equal voltages can be made to cancel each other out — the noise disappears. The second theory is that network cameras transmit video via packets over a 100-ohm balanced media (Category-5e or -6 cables) and therefore no current flow would exist between the two conductors. No current, no possible problem with ground loops. cause bodily harm. As an added note, please measure the voltage if a ground loop is suspect- ed because all correctors are not creat- ed equally. One of the technical aspects of a ground loop isolator or corrector is the amount of AC input voltage the equipment can withstand before it loses its ability to correct a ground loop. T e maximum input voltage for equipment can range from 3.1VAC to 200VAC+. So, measure the voltage of the ground loop before you buy. Figure 2: AC Hum Hum bar Part 4 of 4 Hum bar One source of AC hum is video cable pick- ing up magnetic and electrostatic fields radiated by power wiring. It is caused by proximity to a 100/220VAC power source. CASE NO. 2: INTERMITTENT ISSUES If we apply all the information so far, the distorted image in Figure 2 has the same answers to the questions previously discussed. And the result again would indicate a ground loop. However, in this case, a ground loop corrector would not fi x the problem. What has changed? A4 / SECURITYSALES.COM / OCTOBER 2012 1Courtesy FM Systems