How do I know if my Bag Leak Detection System probe is working?

Posted by Earl Parker on Mar 18, 2015 11:00:00 AM

How to know if my BLDS probe is functioning correctly?

Many customers that use a BLDS at their facility are doing so to meet compliance regulations. When that is the case it is required that periodic checking of the Bag Leak Detection System is performed to insure that it is functioning properly. 

The guidance document from the EPA lists a few of these procedures to be followed:

1)      Electronics Zero/Drift Check

2)      System Zero Check

3)      Response Test 



Some older BLDS will require zero checks of the electronics, and you should consult the operation manual of your equipment to see if it is needed. Since our Unified U3000 is all-digital and incorporates no drift circuitry, we will only focus on items 2 & 3 in this blog.

A typical bag leak detector is made up of three components – electronics, connecting cable, and the probe or sensor. The probes are the components that are actually in contact with the flow stream, transferring the triboelectric effect to the electronics via the connecting cable.

System Zero Check

The purpose of this test is to show that there is no offset in the BLDS when a zero flow condition exists. So it is important that the probe remain isolated in a grounded faraday shield to insure zero flow. This test can be performed in one of two ways: 

  1. When the process is shut down, the best faraday shield can be the grounded duct that the probe is already installed in, as long as there is no appreciable air flow in the duct during shutdown.


  1. You can remove the probe from the duct – keeping it connected to the electronics and place it in a grounded faraday shield. We provide equipment for our customers to accomplish this test – a Field Test Unit along with Probe Test Adapter gives you the means to carry out these tests.

Regardless of the method used, a successful system zero check results in a zero signal observed at the electronics while the probe is isolated. If there is an offset signal observed, the customer would then follow a signal isolation procedure to determine which component is causing the offset.

Response Test

The purpose of the response test is to show the repeatability of the unit over time, insuring that it still provides the same response for a known test condition. Again, there are two methods for performing this test: 

  1. This test is performed by placing a known quantity of material into the flow stream from a test port or similar opening during normal operation of the process.   The test material can be something benign such as Talcum powder, or you can use actual process particulate. Once the known quantity is injected into the flow stream, the unit should be monitored for the response. Once you have performed the test, repeated tests should closely match the initial and future response signals if the material quantity is kept the same.


  1. Using the Field Test Unit and the Probe Test adapter the probe can be removed from the process and placed in the Probe test adapter, creating a zero condition again. The Field test Unit acts as a signal generator injecting a known level of pico amps into the probe to be observed as a signal at the electronics. This response should be recorded and used for future response tests to show proper functioning of the BLDS.

Although these tests are required for compliance , they are also just good practice for proper maintenance of your Bag Leak Detection System and are part of the routine maintenance procedures included in all of our equipment manuals. Proper probe and system maintenance are an important facet of the lifecycle of a triboelectric particulate monitoring device, and these tests and checks will allow for continued accuracy and reliability.

To gather more information on how to optimize the use of Bag Leak Detection Systems check out our Guide To Intelligent Dust Monitoring:

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