Morehouse 600K Light Weight Load Cell System for ASTM E4 Calibration of Concrete Machines
Figure 1 Morehouse Concrete System with High Stability Indicator
This blog is going to discuss the Morehouse Concrete Compression Machine Calibration kit and the potential error sources associated with using a material with a different hardness than what the system was calibrated with. Morehouse has created a kit to minimize the common compression error sources while providing a lightweight portable solution with an ASTM verified range of forces of better than 400 lbf through 600,000 lbf (660,000 lbf is possible) for calibration of concrete machines to ASTM E4.
The calibration kit in figure 1 optimized for calibration of concrete compression testing machines and other testing equipment in the field up to 600,000 lbf. The 600 klbf load cell included in the kit was specifically designed for field applications and it weighs considerably less than a typical load cell at this capacity (28 lbs). Moreover, the kit includes special top and bottom blocks for all load cells which help with better alignment and protect the testing machine platens from concentrated forces.
Figure 2 Morehouse Concrete System with HADI indicator
Concrete Compression Machine Calibration Kit features:
· Compression calibration capability from 400 to 600,000 lbf
· Optional tension calibration capability from 400 to 60,000 lbf
· Less weight, designed for more portability and field applications
· Primary deadweight calibration for 5 and 60 klbf load cells
· ASTM E74 or ISO 376 calibrations and classifications based on user’s requirements
· Highly stable indicator options
· Top and bottom blocks which help with better alignment and protect loading surfaces
The kit includes:
· Morehouse 600 klbf Multi-Column Mini Load Cell
· Morehouse 60 klbf Load Cell with optional tension calibration
· Morehouse 5 klbf Calibration Shear Web Load Cell with optional tension calibration
· One Compression Base Block with alignment grooves for each load cell
· One Alignment Top Block for 600 klbf load cell
· One Spherical Load Button for compression loading of 60 klbf load cell
Now that the features have been discussed, let’s discuss the benefits and error sources when compared with standard calibration set-ups. This kit offers the user a portable, compact, and accurate method for calibration of concrete testing machines while only using 3 load cells.
In our experience, most technicians performing field calibration on concrete machines are struggling with set-ups and often use heavy load cells that are difficult to align, and some may or may not be using the same adapters for the top and bottom of the load cell that they were calibrated with. By not using the same adapters the errors could be quite large.
Figure 3 Hardness of Top Adaptors
In fact, we have observed errors as high as 0.307 % from using different top adaptors as pictured in Figure 3.
Why are the errors so high?
There are two points to make.
#1. Material with different hardness experience different amounts of lateral deflection under the same amount of load. This causes different amounts of stress between the block and load cell
# 2. Flatness and smoothness of the block are important in that it will change the contact position on the load cell. The assumption is the load cell has a radius maybe R17 and is designed to be loaded exactly at the center of the spherical section, but an unbalanced or non-flat block can shift the contact point off center. A small amount of shift will change the stress distribution. The key is to use the same adapters in use as used in calibration. The adapters should be manufactured not to produce off-axis loads. ISO 376 has a lot of good guidance on adapters.
If you want to eliminate the strain from carrying heavy load cells or need a top and bottom block for your load cells to start improving your measurements, please feel free to contact us @ 717-843-0081 or at email@example.com