The digital HST operates at high resolution and more accurate point reflectance during a test than an analog HST. Also, the operator is no longer burdened with manually recording the buzzer trip point reflectance time during a test. A digital HST microprocessor uses an RS-232 serial interface to capture and record all the timed readings continuously, reducing the workload of the operator and allowing for a reflectance reading at every second elapsed until the test is halted. The test results can then be captured and saved in comma separated value (CSV) format, which can then be re-opened into a spreadsheet program and formatted to a curved plotted graph showing the results of the paper being tested. The operator can build multiple graphs for multiple tests runs and plot them into one graph to determine the desired paper sample being tested.
User Calibration Procedure:
Perhaps, one of the most important steps in operating an HST and getting accurate test results is the calibration process that is performed after a machine is given time to properly warm-up for at least 20 minutes then calibrated to the HST’s tile set. This calibration procedure can be daunting on an analog HST mainly due to the aging and wearing of a mechanical needle gauge that can give undesired readings. Gauge replacements are getting harder to come by and more costly to fix for the operator as well.
The digital HST allows the operator to just press ‘calibrate’ button once to calibrate its white tile side and then record the green tile reading. Usually, the HST user will only have to calibrate to a tile set once per power-up. It is good practice to check and re-check tile readings between longer power-up cycles to ensure it hasn’t drifted.
The Tests:
The digital HST will show actual reflectance on display as a sizing test progresses where as an analog does not – the micro amps indicated on an analog meter from the moving meter needle do not show actual intermediate reflectance points. With the digital HST, there is no need to manually adjust a mechanical meter to get an accurate calibration reading. Even further, if a digital HST’s green tile reading was to appear drifting outside it’s acceptable tile set range, then the user can re-dial the tile reading under the digital HST’s service menu back to the original tiles acceptable range without having to send it back to the manufacturer for service and re-calibration. This menu feature allows more service life out of a digital HST. However, we do recommend that a digital HST be assessed every 3 years to determine if there is excessive upward drift. Usually, drift will occur due to excessive heat build-up caused by dust blockage or ink a sensor. It is recommended that a user open and clean the optical assembly, and clean or replace the filter between lamp changes (200 hours). This preventative maintenance will ensure a longer field life between servicing. However, if a user finds themselves constantly having to re-calibrate under the service menu to compensate for upward drift, then this is usually a sign that the HST needs to be serviced and maintenance by a qualified TAF technician. We don’t recommend major field repairs to sensors, cables, or circuitry due to the temperamental nature of an HST to give accurate reliable results.
Analog Drift:
A major reference sensor in an analog runs well into forward bios, which causes signal loss inside the sensor, and improper response to changing illumination levels. The forward bias is also temperature sensitive.
Earlier Analog/Digital conversions:
Some analog HST’s that were designed to be digital have forward bias sensor issues. These early digital models had some forward bias sensor problems – those models we can upgrade with our newer sensors.
A less temperature sensitive sensor in particularly an analog can drift during warm up. This is due to reference sensor forward bias. It also still can respond to any room air temperature changes.
These are mainly just a few advantages of a digital HST will have over an analog. Learn more about the advantages of our feature rich TAF-310 series models and ease of use. Please feel free to contact us if you are deciding whether to upgrade or replace your equipment. We would be happy to assist in this decision.