What’s the purpose of investing in brewery equipment if it is not well calibrated? The most important aspect of calibration is arguably temperature, as temperature during the mashing process has a profound impact on the finished product.
For HERMS breweries, there is an additional aspect of this calibration – what must the temperature differential between the hot liquor tank and the mash lauter tun be to maintain (or increase) mash temperature. This question is system and environment specific. In general, the more opportunity for heat loss, the larger this differential is required to be. When your brewery controller has graphing capabilities, such as one powered by StrangeBrew Elsinore software, this is straightforward to find. Assuming strike temperature is reached through heat exchange with the hot liquor tank, the temperature lag between the mash lauter tun and the hot liquor tank when approaching target temperature is a good starting point. More accurately, this temperature should be the difference in the steady state temperatures of the two vessels under regular recirculation conditions (recirculation speed, quantities of water and grain). Even more accurately, a well tuned PID should be able to control mash temperature through your HLT without any assumptions of a fixed differential between the two vessels.
Depending on the position of your temperature sensors you may have discrepancies in the temperatures reported and the actual temperature of the vessel contents. This is often the case for inline temperature probes (what I currently use) due to heat loss. You may wish to offset this temperatures to be more representative of your mash temperature, for instance. This can be checked against high quality digital thermometers. Probe relocation may circumvent this issue entirely.
To obtain accurate temperature readings and to prevent temperature stratification it is important that vessel contents are well mixed. Regular stirring of the mash, whether it is recirculated or not is of principle importance. If utilizing mash temperature control through a hot liquor tank in some manner, this water should either be recirculated or mixed regularly as well.