The bath uniformity is measured radially, and this measurement is performed with at least two probes. One probe will be designated as the center probe (reference) while the other will be the radial probe. If necessary, a second radial probe can be used to measure at a second immersion depth.
1- Before starting a uniformity test make sure the fluid in the bath meets the required level. In addition, do a visual inspection of the fluid for any changes in color.
2- Create a baseline by placing all probes at the same depth and in close radial proximity. Then adjust the temperature of the radial probes by adjusting the RTPW coefficient to read as close as possible than the center probe (reference). A difference of 0.003°C or less is ideal between the center probe (reference) and the radial probes.
3- Move the center probe (reference) to the center and then position the radial probe to its first position at the desire depth. Positions for the radial probe could be at each hole or 12, 3, 6, and 9 o’clock.
4- Wait for about 20 minutes before start gathering the data and take at least 20 readings. It is also helpful to record the standard deviation to determine how stable the probes are. A standard deviation limit of 1 means that 66.6% of the readings fall within ± one standard deviation.
After all the readings have been gathered, analyze the data to determine if the errors are within the limits.
Bath uniformity data collection example: