A “ghost pour” is a syndrome where Kegbot records a drink that didn’t actually happen (that is, wasn’t actually the result of meter activity).
This article is a work in progress. Last Updated: July 29 2014.
Causes
The prevailing cause of ghost pours is electromagnetic interference (EMI), which gets picked up by the Kegboard and recorded as flow meter activity.
EMI can come from many sources, but the typical source that affects Kegbotters is the refrigerator/kegerator itself: refrigerators motors and compressors generate large inductive loads, and are typically close to the Kegbot electronics.
Sometimes a suspected “ghost pour” has a much simpler explanation:
- Settling/bubbles/meter activity: Small amounts of meter activity can also sometimes a spurious drink to be recorded. This is not common, and can be ruled out through testing (see Diagnosing a ghost pour).
- Short circuit: Never place a Kegboard on a conductive surface without proper insulation; short circuits can lead to unpredictable behavior.
- Moisture: A type of short circuit, moisture on Kegboard, Kegboard Coaster, or cable connections can cause unpredictable behavior. Always ensure Kegbot electronics are kept dry.
The rest of this article will focus on EMI as the primary cause.
Prevalence
We don’t have exact numbers since many Kegbotters run their systems privately and have not reported issues, but empirically we believe most users never experience a ghost pour. This supports our current understanding of the syndrome as occurring largely due to the system’s environment.
Kegboard Pro Mini includes a low-pass RC filter on each flow meter input, which has lowered or eliminated the issue for many users. DIY Kegboard Shields (which do not have these filters) may be more susceptible.
Diagnosing a ghost pour
The following steps are one technique to confirm that EMI is the source of a system’s ghost pour issues:
- Disconnect the keg coupler and drain the beer tubing, but leave the rest of the system intact.
- Wait until a ghost pour is observed. If observed, since meter activity could not have occurred, the source is likely EMI.
- Transport the meter, kegboard, and tablet to another location away from probable EMI sources like the kegerator.
- Repeat step 2, awaiting a ghost pour. If not observed, it’s likely that EMI from the refrigerator is to blame.
Mitigation: Hardware and Placement
The following strategies may mitigate or eliminate EMI issues in your system. Please note that we can not yet recommend a single “silver bullet” that solves the issue.
- Placement: Position your Kegboard, USB wiring, and flow meter and cable as far away from the refrigerator compressor as possible.
- Ferrite bead: Use a USB cable with a ferrite core/bead, which can help dampen high-frequency noise. Snap-on ferrite core clips can also be applied to your flow meter cable.
- Shorten flow meter cable: (Only for DIY users). Use a shorter CAT5 cable; very long cables have a greater susceptibility to EMI.
Additional Resources
There is an open topic in the Kegbot forum for discussion related to this issue.