Grain Systems PNEG-1935 - Manual (Page 42)

6. Moisture Control Options
42 PNEG-1935 Vision Hybrid for Portable Dryers
Moisture Controlled Schemes
The moisture controlled schemes use the exiting moisture sensor as a reference parameter. As the grain
moisture content varies, the controls adjust the unload rate accordingly.
For example, our outgoing (dry) moisture setpoint will be set at 15%. If the outgoing moisture sensor
reports a reading of 16%, the grain is 1% wetter than we desire. To account for this, we decrease the
unload rate, therefore increasing the amount of time the grain is in the heating chamber. The relationship
between moisture and unload rate is inversely proportional. As the exiting moisture increases, the unload
rate should decrease.
5 Speed Moisture
When to Use:
For use with a wider moisture variation spread and for when a moderate reacting moisture control is
desired in all heat operation. Not recommended for dry and cool operation.
How it Works:
The user should stabilize the dryer with the Unload switch in the “MANUAL” position. It is imperative that the
dryer is outputting the desired moisture content grain before switching the unload to the “AUTO” position.
There are five Speeds associated with this drying scheme, but the user only selects one unload rate. The
meter roll setpoint is used as the middle or medium speed. The other four Speeds are offsets of the
medium speed, two higher and two lower. These offsets are labeled as follows: Low (LO), Medium-Low
(M-LO), Medium (MED), Medium-High (M-HI) and High (HI). The unload rate is determined by the
difference between the moisture setpoint and the actual moisture sensor reading. If the reading is exactly
that of our moisture setpoint (a zero offset), MED would be selected, because we must be at the
correct speed.
When setting up the 5 Speed Moisture scheme, there are two (2) sets of parameters: “Inner” and “Outer”.
Both have a moisture and meter roll speed associated with them. “Inner” refers to the M-LO and M-HI
speeds, while “Outer” refers to LO and HI.
Let’s pretend we have the parameters set as they are presented in the following table.
We will set the meter roll setpoint to 50% and the dry grain moisture setpoint to 15% for convenience.
If the dry grain moisture is actually 15%, the MED unload would be selected (50% in our example). Should
the dry grain moisture climb to 15.2%, the controller would change to M-HI, which increases the unload rate
by 3%. Now the dryer’s unload is running at 53% (50% + 3% = 53%). If the dry grain moisture continues to
climb, reaching 15.5%, HI will be selected which increases the unload rate by 12%. This 12% increase is
in relation to the MED speed, NOT the M-HI, so the unload rate is now at 62% (50% + 12% = 62%). If the
dry grain moisture falls back below 15.5%, the controller changes back to LO-HI.
The same is true for dry grain moistures below the setpoint, only the values are subtracted rather than
added. If the dry grain moisture falls to 14.8%, the controller will select M-LO, changing the unload rate to
47% (50% - 3% = 47%).
The following table depicts how the controller would act when setup as the example above.
NOTE: These are not necessarily the values that should be used with this scheme; these numbers were
chosen strictly for explanation purposes.
Inner (M-LO and M-HI) Outer (LO and HI)
Moisture 0.2% 0.5%
Meter Speed Offset 3% 12%
LO (Outer) M-LO (Inner) MED M-HI (Inner) HI (Outer)
Grain
Temperature
Less than or
equal to 14.5%
Between 14.6%
and 14.8%
Between 14.9%
and 15.1%
Between 15.2%
and 15.4%
Greater than or
equal to 15.5%
Unload Rate 38% 47% 50% 53% 62%