Delta OHM HD45 Series Manual page 18

If threshold A value is greater than threshold B value, the contact is closed if the
measuring value rises above threshold A value or falls below threshold B value. The
contact is open if the measuring value is within the two threshold values.
If threshold A value is lower than threshold B value, the contact is open if the
measuring value rises above threshold B value or falls below threshold A value.
The contact is closed if the measuring value is within the two threshold values.
6. Relay activates below threshold B with hysteresis
The contact closes if the measured value falls below threshold B. Contact opens
if the measured value rises above the threshold value plus the hysteresis (B+H).
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