It might be confusing when trying to determine what items need to be sent in for calibration on a 2485 Piston Gauge and/or determining where these items are reported on the Calibration Certificate's. It is also important to send in the Weight Table assembly and Tare Disc's as there are not only a mass value that is needed, but also changes the Effective Area since mass values are used in the cross floating calculations.
The pistons and masses would usually be sent in for calibration and this is fairly obvious as there are slots in the mass shipping boxes for all these as shown in the User Manual graphics for the shipping boxes:
The Pistons have their own container. This container will hold the piston shaft inside the cylinder only:
The Mass also consists of the Hanger Mass (Mass Bell/Carrier) and want to make sure it is sent in for calibration.
There might also be another mass for each piston that is called the Tare Disc. This mass needs to be sent in for each of the pistons being calibrated and would go in the open circular slots that are not not labeled below but have been highlighted:
The Tare Disc sits on top of the Weight Table assembly and are always used when the piston that it is matched to is installed. It is thus part of the Piston calibration and shown as such on the calibration certificate as one of the components that makes up the Total Tare (Total Mass) value for the Piston:
*** Older User Manuals have the Tare Disc labeled as the Tare Mass Compensator Disk
The Weight Table assembly also needs to be sent in for calibration as it rests directly on top of the Piston shaft. It is thus part of the Total Tare Piston mass and also shown on the Piston calibration certificate as one of the components that makes up the Total Tare (Total Mass) value for the Piston:
It is also It is easy to overlooked sending in the Weight Table assembly for calibration as it is part of the 2485 Pressure Column/Piston Mounting Post that gets disassembled to remove the Piston. It consists of four pieces as shown below:
The #3 piece is normally pressed into #2, so it is really three pieces to send in for calibration:
#1 = Table Support
#2= Table Mass (Mass Loading Table)
#4 = Screw
*** There is normally three disks (one bearing and two spacers) that sit around the #1 Table Support shaft, but these can be removed so are not floating during shipping as they are not calibrated items or part of the total Piston mass.
*** There is not a slot in the shipping boxes for the Weight Table assembly so this is also why it can easily be overlooked for shipping in for calibration. It can typically be wrapped in soft paper towels or similar and placed within the open area of the Hanger Mass shown in the first picture above so that it does not need to be shipped separately.
*** If the Weight Table assembly is not shipped in for calibration we try to make contact to verify if this might have been a mistake, but if we do not receive an answer we use our Weight Table to complete the calibration. The end result would be that the calibration certificate and WinPrompt CD will not contain the Weight Table value and the Total Tare/Total Mass value will be very different which leads to significant measurement error if not realized. It is also very important to note that the Weight Table mass value is also used in the Effective Area calculations when cross-floating a piston, so it changes the calculated Effective Area of the piston on top of the significant difference in total piston mass. We do it this way as some labs have mass capabilities to calibrate it themselves and make the corrections, but this is not a simple process.
*** If the Weight Table is not shipped and later returned to us for calibration it cannot be used to just modify the previous Piston Calibration Certificate. A separate calibration report for the Weight Table mass only would be sent and Effective Areas of the pistons would need to be re-calculated. This can only be accommodated upon special request and Management approval as not a standard process and would be additional charges. New WinPrompt CD's would also needs to be generated with the new values.
*** If the Weight Table is not shipped and later returned to us for calibration with the requirement of getting a typical Piston calibration certificate that shows the new Effective Area and proper Total Tare/Total Mass including the Weight Table on the same calibration certificate, the only option is to completely re-calibrate each piston.