Grasso
Refri
eration Division
GRASSO SYSTEM CONTROL
01.2004/1 638660E_chapter2.doc Chap. 2 - 3
2.3.1 Start to start timer (anti- recycle timer)
As electric motors are particularly highly loaded during the start up process, it is important to comply with the
manufacturer’s requirements regarding the allowed number of starts per hour.
These include protection for maintaining the thermal and mechanical loading within limits.
The ’Start to start’ timer fulfils the following function:
• Limitation of the number of starts per unit time.
The permissible number of starts per hour is based on the motor manufacturer’s values for the operating mode
and insulation class.
Output — compressor motor on
’Start to start’ timer active
Compressor motor start not allowed
Figure 2.2, ’Start to start’ timer
A.. The compressor motor ran longer than the ’Start to start’ timer, next start is allowed immediately.
•
If
(1) Compressor motor is switched off
→
and
(2) ’Start to start’ timer has expired
→
Then
(3) Compressor motor start is allowed immediately
B.. The compressor motor ran less than the ’Start to start’ timer, next start is not allowed until the
remaining ’Start to start’ time has expired.
•
If
(1) Compressor motor is switched off
→
and
(2) ’Start to start’ timer still active
→
Then
(3) Compressor motor start is not allowed
2.3.2 Stop to start timer
A minimum time difference is required between a stop and the next start of the compressor motor.
At the same time, the switching device contacts have time to open correctly!
Output — compressor motor on
Feedback — compressor motor on
Stop to start delay active
Figure 2.3, ’Stop to start’ timer
•
If
(1) Compressor motor is switched off
→
and
(2) no feedback compressor motor on
→
Then
(3) ’Stop to start’ delay timer active
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