PTB 311E
3-in-1 Hardness, Diameter and Thickness Testing Instrument

The PTB 311E is the only tablet testing instrument worldwide, which is capable of measuring thickness (height), diameter (length) and hardness of a sample without the need of any additional tools are change-over parts. To assist the user during the thickness testing stage, different jaws to help keep the sample in a vertical position are available. For the hardness and diameter tests the standard jaw size 2, which is supplied in the standard delivery scope is sufficient for all tablets with a thickness from 8 to 12mm.

PTB 311E is designed to test the hardness of any solid sample up to 300 or alternatively 500 (PTB 511E) or 800 Newton (PTB 311E-800) and to be easy to use. The instrument meets the requirements of the current EP <2.9.8> and USP <1217> Pharmacopeia. The test results are immediately displayed on the bright and well legible LED displays of the instrument. PTB 311E is a dual force mode instrument that offers the possibility of testing the hardness of solid in either adjustable constant force or constant speed mode. The instrument is equipped with a printer port to record the results and a RS-232 COM-port for data transfer. We offer the optional PTB32 software package to store and handle the results from the PTB 311E instrument. An upgrade to add 21 CFR Part 11 compliance to the PTB32 software is available as well.

Operating Principle

Enter the nominal test information for thickness, diameter and hardness as well as a batch number via the PTB 311E keyboard. Select the unit to measure, KP (Kilopond), N (Newton) or Sc (Strong Cobb), now place the sample onto the sample dish and start the test. The force jaw will move forward, touch the sample and measure the thickness. By moving back again the sample is moved into a lying position. The jaw moves forward again and touches the sample to measure the diameter. Then the PTB 311E starts to apply force to the tablet until it breaks. This way the hardness (tablet breaking force) is measured. Once all samples have been tested, simply press the <STOP>-key and automatically the results including statistical information are printed via a connected printer. The auto re-start option allows a faster test and higher throughput of samples compared with a manual start procedure. Depending on the actual tablet hardness you can test between 6 to 10 samples per minute.

The flexibility of the instrument and the reproducibility of the results have made this and other models of this series become one of the most sold tablet hardness testing instruments worldwide.


PTB 311E offers an integrated program for adjustment and 3-point calibration. For the static adjustment of the built-in digital load cell a certified 10kg reference weight is required. Static calibration and qualification of the load cell is performed using certified reference weights of 5, 10, 15, 30 and 50kg. To calibrate the breakpoint detection and reproducibility of the instrument we offer the PT-MT3 magnetic test tablet. PT-MT3 is also used for a dynamic calibration of the load cell, instead of using the reference weights. Dedicated reports document the validation of the instrument.

A Note on Calibration and Regulatory Requirements

The current USP Pharmacopeia requires the force sensor of a tablet hardness testing instrument to be calibrated periodically over the complete measuring range (or the range used for measuring samples) with a precision of 1N. All Pharma Test tablet hardness testing instrument can be statically calibrated over the complete measuring range by the use of different tracebale counterweights. All instruments support the checking of at least three different points during calibration to prove the linearity of the force sensor. Furthermore, Pharma Test offers the PT-MT magnetic tablets to calibrate the breakpoint detection of the whole tablet hardness testing instrument (force sensor and mechanics of the instrument). All Pharma Test tablet hardness testing instruments are fully compliant to the requirements of the current USP Pharmacopeia.


  • Fully USP <1217> and EP <2.9.8> compliant
  • 300, 500 and 800N max. hardness range models available
  • Test thickness, diameter and hardness of a tablet
  • Dual force mode instrument with linear speed increase and linear force increase modes
  • Multiple point validation procedure for all three stations built-in
  • Programmable print-out of force increase curve
  • Set to test tension strength of oblongs and caplets available
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