Ask The Expert

It is common for lab managers to create a test procedure that requires the operator to zero or some call it “Balance” or “Tare off” a load cell before the start of a new batch of tests, others insist on zeroing the load cell before every specimen. I believe that either procedure is acceptable, as long as one rule is followed: never zero the load cell with a specimen in the grips. Tinius Olsen load cells are very sensitive and can detect a change in load as a result of gripping the specimen. If the load is zeroed after a specimen is gripped, you risk zeroing off part of the ultimate tensile load. This initial load will be subtracted from (or added to) reported results and can falsely increase or decrease actual values (depending on whether or not there was a compressive or tensile load on the specimen before the load cell was zeroed). If you notice this change on the load channel display after gripping, operators have the option of using automated software features, such as preload (see the software help files for more information) or can manually adjust the position of the crosshead.