Technical Article

Decoupler Testing – Direct Test

Testing instructions for Dairyland products are often requested by customers as a way to verify decoupler operation. For a simple yet effective method of decoupling all Dairyland products refer to: Dairyland Product Testing – Indirect Test

For a direct test, follow the instructions below.


  1. If the decoupler is in service, first disconnect one lead from the decoupler
    1. For pipe to ground installations, it is recommended that you disconnect the pipeline connection.
    2. For insulated joint applications, either lead may be used.
    3. Take appropriate safety precautions, so that the product is isolated.
  2. Next, momentarily short out the device terminals to remove any residual charge that may be on the capacitor within the decoupler. Remove the screwdriver before proceeding to step 3.
  3. Connect a multi-meter, set to the lowest Ohms scale, across the terminals.
    1. If the product is functional, the resistance will start at zero ohms and then very slowly increase as the capacitor in the decoupler begins to charge from the multi-meter. You may discontinue the test at this point, as charging the capacitor can take up to 10 minutes, and it is only necessary to observe this general response briefly.
    2. If the product is failed, the reading will remain fixed and at a very low resistance value, typically a fraction of one Ohm.


Testing PCR


Models OVP, OVP2

The models OVP and OVP2 block both AC and DC under normal conditions, before switching to the shorted mode. A direct test of the products can be made, and it differs from tests of the decouplers mentioned above.

  1. Disconnect one lead from the device.
    1. If the product is functional, the resistance will immediately read a high value, typically hundreds of kilo-Ohms or greater
    2. If the product is failed, the reading will remain fixed and at a very low resistance value, typically a fraction of one Ohm.


Testing OVP


Important Safety Considerations

Take appropriate safety measures before disconnecting any Dairyland decoupler and contact Dairyland for further assistance if additional information is necessary to assure that safe practices are used. Refer to the Installation and Operating Instructions for full information.

If the Dairyland device is performing mitigation of induced AC voltage, disconnecting the device will leave the structure as an open circuit, and the induced voltage on the pipeline may rise above the 15V safe level established by NACE guidelines.

A shorting jumper cable connected between the two leads before one of them is disconnected from the decoupler will prevent any voltage rise on the structure. Alternatively, the jumper can be connected between the same two structures as the decoupler leads. At insulated joints, a jumper should be connected across the joint prior to disconnection of a decoupler if AC voltage is present.

When a decoupler is used to provide ac grounding of electrical equipment (e.g. motor operated valve) in a cathodically protected pipeline, a shorting jumper must be connected between the two cables connected to the decoupler so as to keep the equipment grounded when a decoupler lead is removed for testing.

Based on the extensive product history and design, it is not expected that Dairyland product failures will be encountered. If the above tests show the product to be functional, yet cathodic protection readings imply that a problem exists, consider the following possibilities:

Open circuit voltage too high:

If the CP voltage (or total DC voltage from all sources) is above the threshold voltage of the Dairyland device, the device will switch into the conduction mode for protection, which would affect CP readings. If this occurs, it is typically near a rectifier ground bed. Solution: select the same Dairyland product family, but with a higher threshold voltage.

OVP or OVP2 used where induced AC present:

The OVP and OVP2 are not designed to be used where induced AC is present. Installation with induced ac present will cause the device to switch to the conducting mode potentially impacting CP voltage. Switch to models SSD, PCR, or PCRH to accomplish AC mitigation while blocking DC.

Insulating joint protected by decoupler fails radio frequency insulation test:

A Dairyland decoupler will appear as a short circuit to a radio frequency test device connected across an insulator. To test the insulator alone, remove the Dairyland device first, considering the safety issues discussed in this article. The Dairyland device can then be checked separately as discussed above.

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