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I operate in a wastewater treatment plant laboratory and I use respirometric method for BOD5 measurement (hach direct plus). Recently I am obtaining high value for BOD (biological oxygen demand) for example BOD5 581 mg/L when the COD (chemical oxygen demand) of the same sample 895 mg/L. I did multiple assays on another sample and I obtained different values for the same sample using the same initial volume (209 mg/L and 586 mg/L while COD 630 mg/L). I thought that some sensors are not functioning properly. I want to know if these pressure sensors can be calibrated, anyone can help please??

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  • $\begingroup$ You might want to provide more information on what specific sensors you are talking about (make and model). $\endgroup$ – Buck Thorn Sep 5 '19 at 20:51
  • $\begingroup$ @Buck Thorn I did, thank you for notifying $\endgroup$ – Shafik Saad Sep 6 '19 at 18:37
  • $\begingroup$ Just to confirn, you mean this: uk.hach.com/other-instruments/bod-direct-plus/… ? $\endgroup$ – Buck Thorn Sep 7 '19 at 5:46
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    $\begingroup$ @Buck Thorn yes the manual you are reading is the true one. I think I am experienced with the device because I am using it from about 2 years in 2 different laboratories and I am facing this problem only with one of them. I took a sample to the second lab and used the second equipment and obtained better results. I am just asking for someone who used this equipment before to see if there is any calibration method for the sensors. Anyway thank you so much for your help $\endgroup$ – Shafik Saad Sep 10 '19 at 6:10
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    $\begingroup$ @Buck Thorn, many thanks for your help, I contacted the supplier and have been told that the sensors can't be calibrated maybe the problem is in the direct plus apparatus. Anyway I will send the equipment to the supplier and they will work to fix it. Thank you for your help. $\endgroup$ – Shafik Saad Sep 11 '19 at 7:34

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