The Sentrymultizone is a multi-zone corrosion monitor.  An LCD display and LED’s provide indication of the cathodic protection level.

The multizone capability of the Sentrymultizone allows different zones on a structure or vessel to be simultaneously monitored. For example, the external hull may represent one zone, other zones may include the insides of sea chests, ballast tanks, water jet tunnels etc. Each zone requires a reference electrode to be installed. Up to 3 zones can be monitored with one Sentrymultizone .

The Sentrymultizone kit comprises a Sentrymultizone monitor, mounting screws, 3 AA batteries, and an earth lead.

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Sentrymultizone kit


Note: Reference electrodes are purchased separately. Refer to: Reference electrode installation and Order information

  1. The Sentrymultizone can be bulkhead mounted in any convenient location such as in the engine room or in the vessel’s bridge/pilot house.  The box dimensions are 115 mm x 65 mm x 40 mm deep.
  2. Drill two 3.8mm diameter holes at 83.5 mm by 52.5 mm centers on the hull bulkhead or other suitable mounting location. See the schematic drawing of the Sentrymultizone below.
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    Schematic of Sentrymultizone with wiring and installation details
  3. Remove the Sentrymultizone lid taking care to keep it supported. Mount the Sentrymultizone box using the two 8g x 12 mm self tapping screws provided. 
  4. Insert the 3 AA batteries supplied. Refasten the Sentrymultizone lid.
  5. Connect terminal E to the hull with the earth lead provided.
  6. Connect terminals 1 up to 3 to reference electrodes.

Monitor operation

Press the test button. The LEDs will light and LCD milli-volts will display.  The Sentrymultizone will commence reading zone 1. After a few seconds the Sentrymultizone will cycle to zone 2 and so on. To conserve battery life the Sentrymultizone operates normally in ‘power down’ mode. The Sentrymultizone will auto power down after one minute.  

For a particular zone, a reference electrode must be connected to the corresponding terminal on the Sentrymultizone and it must be in contact with sea water. Only then will the Sentrymultizone indicate the cathodic protection level correctly.    

Cathodic protection levels

The Sentrymultizone has LCD and LED indication of the cathodic protection level. Providing the Sentrymultizone has been set up for the correct material and reference electrode type, green LED indication shows that the material is protected form corrosion. Red LED indication can indicate under protection or over protection. Under protection indicates corrosion can take place. The rate of corrosion is influenced by a number of variables such as the type of material, the oxide layer present, the quality of the electrolyte and the potential relative to the reference electrode.  Moderate over protection can be accepted but may be uneconomic for steel, bronze and brass.  Over protection can cause problems with aluminum due to amphoteric attack.

LCD readings can be evaluated from the table below for Seaguard zinc electrodes and typical materials in use in the marine sector. For Ag AgCl reference electrodes, subtract 1000 from the numbers below:


Freely corroding


Over protected

Carbon steel




304 Stainless steel (active)



















115 x 65 x 40mm



Operating temp.

0 to 500 C


-1200mV to +1200mV


+/- 5 mV


IP 65


Up to 3 zones

Battery life

>2 years

Ref. electrode

Zinc or AgAgCl (1, 2 or 3 required)


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