Danfoss EKC 331T User guide

Capacity controller

EKC 331T

Manual

Introduction

Application

The controller is used for capacity regulation of compressors or
condensers in small refrigerating systems.
Regulation can be carried out with up to four identical capacity
steps.

Advantages

• Patented neutral zone regulation

• Sequential or cyclic operation

Functions

• Regulation

Regulation with up to four relay outputs can be carried out.
Regulation takes place with a set reference which is compared
to a signal from a pressure transmitter or a temperature sensor.

• Relay module

It is possible to use the controller as relay module, so that the
relays are cut in or out by means of an external voltage signal.

• Alarm function
A relay becomes activated when the set alarm limits are ex­ceeded.

• Digital input
The digital input can be used for:

- night operation where the suction pressure is raised

- heat recovery where the condensing pressure is raised

- external start/stop of the regulation.

- Monitoring of safety circuit

• Reverse function

The regulation can be reversed so that the relays are activated
in case of falling temperature, rather than by the rising tempera­ture.

• Possibility of data communication

Display

A signal from a pressure transmitter will always be converted and
shown as a temperature value.
Settings are made as for temperature values.

Function

Capacity regulation

The cut-in capacity is controlled by signals from the connected
pressure transmitter (temperature sensor) and the set reference.
Outside the reference a neutral zone is set where the capacity will
neither be cut in nor out.
Outside the neutral zone (in the hatched areas named +zone and

-zone) the capacity will be cut in or out if the regulation registers

a change of pressure (the temperature) “away” from the neutral
zone. Cutin and cutout will take place with the set time delays.
If the pressure (the temperature) however “approaches” the
neutral zone, the controller will make no changes of the cut-in
capacity.
If regulation takes place outside the hatched area (named ++zone
and --zone), changes of the cut-in capacity will occur somewhat
faster than if it were in the hatched area.
Cutin of steps can be dened for either sequential or cyclic opera­tion.

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Sequential

The relays are here cut in in sequence – rst relay number 1, then
2, etc.
Cutout takes place in the opposite sequence, i.e. the last cut-in
relay will be cut out rst.

Cyclic

The relays are coupled here so that the operating time of the
individual relays will become equalised.
At each cutin the regulation scans the individual relays’ timer,
cutting in the relay with least time on it.
At each cutout a similar thing happens. Here the relay is cut out
that has most hours on the timer.

Rx = random relay
h = number of hours

If capacity regulation is carried out on two compressors with one
unloader each, the following function can be used:
Relays 1 and 3 are connected to the compressor motor.
Relays 2 and 4 are connected to the unloaders.
Relays 1 and 3 will operate in such a way that the operating time
for the two relays will become equalised.

Relay module

The controller can also be used as a relay module where the relays
in the module are operated by the received voltage signal. The
signal must be connected to terminal 15-16.
Depending on the denition of the signal and the number of
relays used, the relays will be ”distributed” over the signal.
A hysteresis at the individual coupling points will ensure that the
relay will not cut in or out when not required.

C = compressor, L = Unloader

EKC 331T Manual RS8CU502 © Danfoss 08-2012 3

Suvey of functions

Function Para-

meter

Normal display

Normally the signal from the pressure transmitter/temperature sensor is shown
If the controller is used as relay module, Uin will appear on the display.

Pressure regulation Reference Settings

Regulation setpoint

Regulation is based on the set value.
A change of the set value can be limited/xed by means of the settings in r02 and r03.

(Push both buttons simultaneously to set the menu.)

Neutral zone

There is a neutral zone around the reference. See also page 2.

Start/stop of refrigeration

With this setting the refrigeration can be started and stopped. Start/stop of refrigera­tion may also be performed with an external contact function connected to the input
named "DI".

Reference
The set reference may be displaced with a xed value when a signal is received at the
DI input. Regulation will then be based on the set point plus the value set here.
(Cf. also Denition of DI input).

Night setback
OFF: No change of the reference
ON: (1) Oset value in "r13" forms part of the reference

The total reference can be seen when you push the lower of the two buttons - Reference

Reference limitation

With these settings the setpoint can only be set between the two values.
(This also apply if regulation with displacements of the reference).

Max. permissible reference value. r25 Max. reference

Parameter by operation via
data communication

Pressure / Temp°C

- Set point°C

r01 Neutral zone

r12 Main switch

r13 Ref. oset

r27 NightSetback

Min. permissible reference value. r26 Min. reference

Correction of temperature measurement

An oset adjustment of the registered temperature can be made. The function is used
if correction for a too long sensor cable has to be made.

Unit

Here you can select whether the display is to indicate SI units or US units (°C and bar
or °F and psig)
Setting = "C-b" will give °C and bar
Setting = "F-P" will give °F and psig.
All settings made in ° C or ° F. Excluding o20 and o21, which is set in the bar / PSIG.

Capacity Capacity Settings
Running time

To prevent frequent start/stop, values have to be set for how the relays are to cut in
and out.

Min. ON time for relays. c01 Min.ON time
Min. time period between cutin of same relay. c07 Recycle time

Coupling (compressor and condensor)

Cutin and cutout can take place in three ways:

1. Sequential: First relay 1 cuts in, then relay 2, etc. Cutout takes place in the opposite
sequence. (”First in, last out”).

2. Cyclic: An automatic operating time equalisation is arranged here, so that all steps
will have the same operating time. (The relay with the fewest number of operating

hours cuts in or out before the others) (Or put dierently: ”First in, last out”).

3. Compressor(s) with unloader: The cyclic operation is performed on relays 1 and 3.
The unloaders are mounted on relays 2 and 4 (relays 1 and 2 belong to the rst com­pressor, relays 3 and 4 to the other). The above mentioned ”Min. On-time” and "Min.
recycle time" are not used for unloaders.
In connection with cutout, the two unloaders are cut out before the compressors are
cut out.

r04 Adjust sensor

r05 (In AKM only °C and bar is used, what-

ever the setting)

c08 Step mode

Unloaders’ cutin and cutout mode

(Only in connection with cutin/cutout mode 3. See above).
The relays for the two unloaders can be set to switch on when more capacity is re­quired (setting = no), or they can switch o when more capacity is called for (setting
= nc).

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c09 Unloader

(switch on = 0)
(switch o = 1)