Alarms - Danfoss EIM 365 User Manual

Superheat controller, type EIM 365 (PV01)

Alarms

Alarms and troubleshooting
Problems with startup
Sometimes in one-to-one applications, the valve does not open sufficiently on startup, and troublesome low
pressure trips may occur. The force opening of valve function has been implemented in the EIM 336 controller. After
startup, this function will provide a constant, set minimum opening degree during a set time period, regardless of
the superheat value. The setting parameters are called Start OD% (n17) and StartUp time (n15).
Figure 12: Problems with startup
Low Pressure Issue due to compressor cut in and cut out
One of the features of TEX valves is the external pressure equalization making a direct and fast responding pressure
connection between the compressor suction line and underside of the diaphragm in the valve. This enables the
valve to open-/ close momentarily with compressor capacity cut in and out.Thesame function has been
implemented into EIM 336, which is controlled by the parameter n20, KpTo. In this function. kp factor related
directly to the suction pressure (To) with direct effect on the requested signal to the ETS 6 valve .Thedefault value of
KpTo is set to automatic (i.e -1). If the automatic tuning is not fulfilling the desired order, Increasing the n20 setting
to the fixed value will contribute to an improvement. Too high n20 will produce high fluctuation in superheat
regulation.
Fluctuating superheat
When the refrigerating system has been made to work steadily, the controller's factory-set control parameters
should in most cases provide a stable and relatively fast regulating system. If the system however fluctuates, this
may be due to the fact that too low superheat parameters have been selected or due set of regulation parameters
which are not optimal
Usually,the following parameters can be tuned in order to reach fast, stable superheat in EIM controller.
• If adaptive superheat has been selected adjust n09 and n10 parameters. For some application using fixed
superheat may increase the stability. This can be done by defining n09 and n010 to the fixed value.
• To optimize the superheat regulation, most safe and direct way is to tune TnSH. For example, if a the control is too
slow, define new Tn value to half (1/2 Tn), if it is still slow reduce it to another half (1/2 x 1/2 Tn= 1/4 Tn), If the
control start to oscillation, then return back to (~ 3/8 Tn) ,alternatively read the time period and tune tn = 1.2 x
time period.
• Keep KpT0, Alpha as default, they work for most of the cases.
• Tune parameter for force opening of the valve at start up i.e. n15 (startup OD) and n17 (start up time). These values
depends on the system conditions.
 NOTE:
Steps (1.) to (3.) are quite easy and safe to tune. For step (4.), caution should be taken, so as not to allow refrigerant
inside the compressor.
Too high fluctuating pressure signal
1. Tune parameter n20 KpT0 to lower value, if this is not working for the system disable by setting it to zero.
2. If point 1 doesn't seem to be working, then keep n20 KpT0 disable and increase para TSH (i.e Tan SH). Increase
TSH (default value) by 200 and check the oscillation. If the problem seems to persist, perform the same step up
to higher TSH value.
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