this is an introduction to the a K to 55 system controller by Danfoss the light at the top can be used for alarming in which he’ll turn red or green to indicate that there’s no alarms this function can be turned on or off the display is a VGA display and requires no contrast adjustment the keypad has several functions function keys f1 through FN can be assigned in specific menus f2 can be used in any screen to access the access code option you’ll be prompted for your authorization code and account code the Menu key will always take you back to the main menu the Edit key is typically used to make changes to fields the Direct Connect adapter connects here this allows communication between the 255 and your laptop or PC using the Danfoss a KA 65 software connect your direct connect cable here ul regulations require that the door of the a K 255 is a lock device that cannot be opened without a tool to open the door insert a slotted screwdriver quarter or other device to release the mechanism here’s an overview of the inside of the Danfoss a k2 55 here you’ll find we have the base board and CPU board combination the CPU is the smaller board and contains the sticker with the MAC address of the controller this board is the inverter for the backlit display and the display is found here on this side we find the input board where inputs come into the unit also communication connections are made on this side we have the power supply you let’s take a look inside the details of the a k2 55 controller from danfoss first we’ll look at the base board and CPU combination here you’ll find the three volt lithium battery just above the battery is the battery jumper the board is marked with three terminals one two and three to retain the settings in the controller the battery jumper must be across pins one and two next we’ll look at the rotary address switch which is used to give the 255 it’s number addresses always start at 0 and can go as high as 9 here we find the rs-485 function jumpers these would get removed under normal situations unless you’re using Modbus rs-485 IO nodes here we’ll find the USB connection which can be used for loading software saving programs and downloading programs into the controller the CPU reset switch for the 255

controller is found here pressing at once will reset the controller and restart all functions the power supply board for the danfoss a k2 55 is found here moving down through the controller we see the incoming power which can be any voltage from 100 to 240 volts ac next we find five ports for i/o connections these RS lan-based the connector for the rs-485 communication is found here it is polarity sensitive note the terminals marked dy and DX this connection is for the internal alarm relay here we find the modem connection and finally the ethernet connection you let’s take a look at the a k2 modules used for i/o communication to the danfoss 255 here you see the 24 volt DC power supply next the communication module this module will start each group of boards this module is usually known as the combo module this one has eight inputs and eight outputs for relays this board is used for inputs or dry contact digital inputs next you’ll see the danfoss stepper board the stepper module can drive for stepper valves this is a pulse module used to read up to eight pulse inputs typically from kW meters and lastly this module reads for analog inputs or for digital inputs at the top and provides for analog outputs at the bottom you this 24 volt DC power supply can be powered with AC voltage from 100 to 240 volts it provides to 24 volt DC outputs this green indicator light means we have power coming to the power supply and the output is not shorted if the output would be shorted this green light will go out until the short is removed moving on to the communication module you’ll see the pattern of lights here indicates good communication status one should blink status 2 & 3 should be on steady along with the power light at the top we have the 24 volt connection this module can be powered with either 24 volts AC or DC the other connector is for i/o communication back to the Danfoss 255 note the location of the termination resistor since this module is the end of the i/o loop the cover of this module and other modules can be removed by squeezing the right and left side and

pulling toward you this reveals the fuse inside the comm module and gives us a better look at the address switches the address switches are important for setting up IO points this module usually is known as the combo module it contains 8 analog inputs or 8 dry contact digital inputs at the top and 8 relay connections at the bottom this is what’s considered a full-size module there’s three modules that are full-size this combo module another module which is relay only and the stepper module at the top you have eight inputs that can be used for pressure transducers temp sensors 0 to 10 volt inputs and dry contact digital inputs there are two locations where plus 12 volts DC is provided to power sensors along with a +5 volt location for sensor power some modules may be equipped with recessed override switches to override a load simply move the switch to the left or the right depending on whether the load should be turned on or off when the load is turned on or off indicator lights on this side will remind us that we are in override and the green light will indicate whether the relay coil is energized or de-energized right now our indicator lights tell us that relay number 4 is in override and the relay coil is energized relay number 5 is in override but the relay coil is de-energized to remove the cover to get to the fuse locations first D power the communication module next squeeze the right and left side plastic strips and pull toward you here we see the location of the five amp fuses to return power to the board replace the override switches in the cover and power up the communication module here you see the terminal strip for connecting the loads to the combo board each load gives you a common normally open and normally closed connection relays on the board are fused at 5 amps and 230 volt is the limit next moving to the analog input board you see a very similar arrangement for inputs the commlite would turn red if there is a communication problem with the a K 255 the bottom row also contains inputs but in a reversed fashion when in doubt remove the cover look at the legend on the bottom if there’s a question about a wire hook Oh here you see another type of module this is a half size module and is used to provide for analog or dry contact digital inputs at the top and for analog outputs at the bottom the 255 will allow you to configure your analog outputs for either 0 to 5 volts 0 to 10 volts or 10 to 0 volts DC next you see the pulse module used for

reading pulses from kWh meters and other pulse output devices we have four inputs at the top and four inputs at the bottom and lastly the stepper module power for the valves themselves are provided at the top 24 volts DC or 12 volts AC will be wired here to power the valves indicator lights shown here will indicate if each valve is opening or closing connections to each valve are made here wire polarity is important consult the manufacturers diagrams based on the valve you are using you let’s take a look at the communication module used to communicate to a k2 modules at the top we have the power and communication connections for TP 78 communication such as this communication modules must be daisy-chained the resistor shown here was removed from the plug inside the a k2 55 and placed at the last module on the daisy chain this module can have nine modules plugged into it upon powerup it will recognize the modules installed address switches at the bottom set the address for the communication module upon powerup the communication module will recognize the position of each board board number one is shown here board number two is shown here in this example we have the address dials set to 0 0 of 1 which means with this being our first load the relay assignment would be 1 – 1 and point 1 you next we’ll cover replacing or adding an a k2 module note that on each a k2 module the part number can be found here should it be needed the first step is to depower the communications module this is an important step otherwise the module could be damaged first we’ll remove any connectors with wires attached to remove the module first we must unlock the tab from the din rail its first starting at the top then the bottom you’ll note that the red tab stays in place this indicates that the module is unlocked from the din rail next lift the module directly toward you to reinsert a module first line up the z connector then push the module into place it’s important that it’s lined up with other modules on the group to lock the module to the din rail press the red tab at the bottom and the top the last step is to reconnect any terminal strips and reapply power

this condition indicates a communication loss between the a k2 modules and the 255 controller note on the communication module status one is on steady this is not a normal condition and the error light is lit on extension modules note the red blinking comm light this indicates communication with the host controller which is the 255 has been lost to troubleshoot this condition wiring and voltages must be checked here you see the normal status has been restored on the communication module status one is again blinking and the error light is now out on extension modules the red comm light should be out to indicate proper communication today we’ll be looking at rack control condenser control and circuit control along with other features of the Danfoss a k2 55 controller let’s talk about authorization account codes passwords and audit trails in the 255 controller you can enter an access code at any time by pressing the f2 button on your keypad you’ll see a screen pop up like this asking for an authorization code and an account code let’s log out and log back in so we can see how this works once again you may press the f2 button and be prompted for a code after each set of numbers you must hit enter you can verify that your code was accepted by pressing the f2 key once again this will display your level of authorization another way to log in is by going to the authorization screen this will allow entry of your authorization code in your account code remember to hit enter or ok after each entry of the code or account code it’s possible to log out in this screen and it’s also possible to view the audit trail the audit trail can be viewed without an access code and displays the contents of changes made when they were made who made them and whether they were made via network modem keypad or a direct connection from a laptop it’s possible to get an overview of the refrigeration system by first selecting refrigeration the rack then rack overview this screen shows us the status of compressors condensers and circuits along with displaying the refrigerant oil type if programmed suction pressure and discharge pressure here you see the status of each condenser fan compressor and evaporator it’s possible to get more details on any of these items by selecting it to backup escape will take you back to the overview we can get more details by selecting an evaporator paging down here you’ll find defrost runtimes refrigeration runtimes cycles last defrost cycles let’s back up take a look at the rack overview screen and see the cycles and run times for condenser fan the relay number 5 you

here you see the list of evaporators and sensors their current temperatures and targets the address in the middle is the board point or the sensor is connected to the a K 255 input board if we want to find out what defrost times are programmed into the 255 we can check the defrost map this will list all defrost based on a 24-hour schedule here you can see most Glassdoor cases or using a staggered defrost time walk-in freezers are using multiple defrost per day or staggered schedules to minimize overlap let’s look at another feature of the a K 255 called dynamic suction float this option allows the rack to float the suction pressure up when specific cases have reached their target it’s called dynamic because it can switch between several cases to see the settings navigate to configure rack and suction info the suction ID is listed at the top below that will find PSIG target of fourteen point three pounds this is the base target for this suction group this group is allowed to float a maximum of four pounds let’s take a look at how this would appear on the suction group status screen here you can see the new target for the rack is sixteen point five psi based on a float of 2.2 pounds remember 2.2 pounds was added to the base target of fourteen point three let’s view the dynamic float from the evaporator the screen tells us that it’s currently floating based on Glassdoor ice cream case 11 we can see that today it’s floated by 2.2 pounds and so far today it’s been floating on this case 33 percent of the day a listing of all cases that are included in dynamic suction float are listed here as the case would reach its target the rack would be allowed to float to a maximum of 4 pounds as you can see the float has adjusted slightly down to 1.9 pounds giving the rack a new reference point this racks basic target is 16 pounds we know that it’s not floating currently because the float adjustment is set to 0 the reason for this is that the case temperatures that are floating the suction are higher than the target temperature as we’ll see in a moment the case that’s floating the rack is actually in defrost right now let’s take a look at how this floating is set up in the suction info screen we can see that floating is turned on this particular rack is floating based on a board point the board point in this case is a calculation this calculation looks at a target temperature of minus 10 degrees Fahrenheit plus or minus 1 degree as you can see and it’s important to know that the rack cannot float more than 5 pounds as we saw before that means this rack cannot float above 21 pounds psi we know that this board point is a calculation let’s take a look at what’s really going on in this calculation

calculation number one as you can see is used for floating in this calculation we’re taking the average of four sensors in this case it happens to be ice cream glass doors the average of these is 29 degrees because the case is in defrost currently next let’s take a look at services available through the rack service screen available to you the user here you see the rack status screen at the bottom of the screen like many screens in the 255 you’ll find several icons each icon and will take you to another area where you can make changes observe history or just see board points this icon is the service screen here you see options available to you options that you have such as overrides which can be done with Auto manual relays or auto manual inputs or even sensor adjustments let’s take a look at Auto manual relays if we need to override a compressor in this case it can be done through the auto manual operation to do this you would use your edit key to highlight the compressor you need to override let’s say we want to override system 1 a compressor in the on position it select manual on and the compressor will be over at non this override will stay in place until removed by the user there are two ways to remove the override it’s possible to remove it by just hitting or selecting the reset button at the bottom or we can simply go back to the point switch back to auto and the override is removed it’s also possible to override or offset sensors using the service screen let’s go to the sensor adjustment menu here you see several options the current reading is displayed any offsets are displayed and here we see more detailed information about the sensor itself including resistance values and DC voltages seen by the input board let’s take a look at options available to evaporator screens it’s possible to place a case in defrost or even suspend alarms along with offsetting sensors let’s select a sensor as you can see once again you have several options available at the bottom of your screen with icons let’s go back to the service icon to see what’s available here we can Auto manual relays Auto manual digital inputs offset and adjust sensors what cases in manual defrost view or change board points or suspend alarms suspending alarms is done on a per sensor basis for instance if a case has three sensors and you override one sensor only that sensor would be affected the sets are offset screen it’s available much like the rack we looked at to allow offsets to be placed for cases and to view input information let’s say we needed to defrost a case using what’s known as emergency defrost select manual defrost and you’ll see your options for this case the defrost operation can be changed from auto to manual on or manual off the maximum time can be adjusted here if a defrost is needed that is longer than the normal defrost time and here you can select whether or not you want to terminate based on time or other termination options normally afford it

into the case next let’s look at the option of suspending alarm generation per sensor in this case if we switched the status from off to on this case would be suspended for 60 minutes allowing no alarms during that time after 60 minutes the normal alarm generation possibilities would exist next let’s look into the alarms setup of alarms viewing active acknowledged and cleared alarms and determining whether alarms were in fact sent to other parties so that a correct response can be made alarm setup is where most setups are made so that alarms are done correctly routing contains information about how the alarms are sent out from the controller and which alarms are sent from the controller starting at the top you see an alarm relay is activated these action numbers can be defined on any alarm it’s really a way to group alarms into eight different groups because some alarms may be routed in one way and other less important alarms may be routed in a different way here you can see we’ve selected any alarm with action number one to go to an alarm relay here labeled as a relay a there’s no delay before the alarm can activate the relay and the relay will stay on until all alarms have cleared we can find more information about this alarm relay by selecting this arrow to the left of relay a here we see a name was given to the alarm relay called alarm 1 it’s important to note that this alarm relay does not exist on this controller at this site rack 1 is considered unit number 1 but the alarm relay is actually residing on controller 0 so this controller has been set to send its alarms to unit 0 alarm relay defined as alarm 1 if we page down we can see more information about the setup of the alarms here we see that the front LED on the front of the 2:55 will turn red if any alarm exists defined as any alarm action one through eight the relay will not turn back to green until all alarms have cleared next we can look at alarm setups going to modem numbers and networks here you see the first phone number is set to grab action number one alarms after one minute dial those out not send out clear messages and stop dialing out when the alarm is cleared let’s check the setup for the phone number number one here you can see it’s been programmed to dial out to triangle refrigeration using this phone number the person on site or the Installer has determined that to send the alarm out to this number they first must dial nine nine comma the schedule has been set to standard meaning the alarm will dial out any time during the day and any day during the week if the schedule is not set from standard and left and the not use position no alarms will dial out let’s page down to verify that the setup is correct in this case the 255 is programmed to know that the modem exists on unit zero the ethernet is connected to unit zero and there is no alarm logger installed from the main menu we can find information about alarms that may have occurred in the past and alarms that may be in pending mode before you leave the store let’s take a look at the alarms menu seen from the main menu here we have the option to

view active alarms acknowledged alarms and cleared alarms it’s important to note that the alarm status is used by many mechanics and technicians to view the status of alarms that may be pending before they leave the site a useful tool is using the alarm status screen to check for any alarms that may be counting down indicating a problem that could exist here each alarm configured in the controller will be displayed if there are no pending actions the state will read okay you can page down to see all the alarms this indicates that the box door for this evaporator is actually open in the alarm has tripped this particular alarm is set to log only and will only be viewed in the ole active alarm screen if you would find a state reading in a number of seconds and decrementing that would indicate that the alarm is an alarm pending mode and may need to be checked before you would leave the site next let’s take a look at options available in the alarm menu active alarms which show alarms that are active currently and may have stayed there for an undetermined amount of time here you can see the Box door open alarm we saw earlier this will display the settings for the alarm the reading for the alarm when it took place and whether or not the alarm has been acknowledged here we have the option to view alarms that have been acknowledged but are still active in this case there are no acknowledged alarms cleared alarms will display any alarms in the log that have been an alarm but have subsequently cleared here you see several arms for the freezer box we have available 59 pages worth of cleared alarms at the top we can see that there are total of 234 entries in this log it’s possible to acknowledge all alarms but a confirmation must be made to ensure that is correct it’s possible to page down through several pages worth of alarms to find any alarms you might be looking for here we see an alarm for system IC GD 1 – 0 9 it alarmed on January 18th 10:58 a.m. and at the time was reading 36.5 degrees Fahrenheit the temperature currently in this case is negative ten point two degrees Fahrenheit it alarms any time it’s above five degrees for ninety minutes and is not in defrost it’s possible to get more details about this alarm by selecting it this tells us some important information about this alarm for instance we know this alarm is set to dial out to triangle refrigeration and it’s important to note that it did so successfully on January 18 2012 at 10:59 a.m. next let’s look at miscellaneous alarms these may include individual points that don’t fit the current conventions for alarms to access miscellaneous alarms you may view those through the alarm menu or through miscellaneous here you see the normal groupings for i/o points relay outputs sensor inputs on/off inputs vert outputs and other controllers let’s take a look at on/off inputs here you find an alarm configured for system 1 oil fail to view the details of this alarm and how it was set up select the name then you’ll find the number of alarm set and the characteristics of the alarm let’s take a look at history options

when viewing circuits history options will be similar for other screens in the 255 if we check this sensor we see the normal status but like many screens we have other options available at the bottom of the menu the camera icon will lead you to history when entering the screen typical default information will be populated there are several options available and afforded to you at the bottom of the screen for instance we know that the listing of the data will be done at one-minute rates this rate can be changed to better match the setup of the individual point for instance note that at the top of the screen these three points that are important to this evaporator are logged on 10 minute intervals because of that if we view the graph at one minute rates we’re simply going to see duplicated information let’s change this rate to 10 minutes to get better information and more information on the same screen in this case we’re in text mode so we simply see tabular data for the three points listed at the top of the screen other options are graphs allowing you to scroll backwards a page at a time and obviously we could scroll forward in time as well this indicates a case to frost if we want more resolution on the graph we could change the maximum scaling seen on the left side to return to text mode simply select the text button the stat button will give you important statistical information on the three points listed each point listed at the top is given a data point number here seen as DP one two and three we can tell based on the screen that data point number one is the temperature for frozen food Glassdoor three – zero three and it’s important to note that in the last 24 hours through 4:30 a.m. today the minimum temperature was minus six point eight the max temp was thirty seven point five and the average temp in that time frame was negative three point four degrees Fahrenheit the relays are listed here including the refrigeration relay scene as DP – and the defrost relay scene as DP three this information tells us that the refrigeration relay was on completely in the last 24 hours except for the 30 minutes for defrost there was one cycle indicating there is only one defrost programmed for this case and you here will see on percentages for each relay the select button at the bottom will give you options for other i/o points that may be available other important points about history are seen here information about general history setups can be found from the main menu then selecting history here we see that history is being collected other status you may see are not configured or suspended history can only be restarted if found in suspended mode with a supervisor access code it’s possible to verify that points are being recorded in history by selecting configure history

then setup history data points here you can see a listing of all points the sample rate in this case is set to 10 minutes for each point if we page down through the relays will be given a display of each point and we can see if there are any points that are not being logged in history a point not being logged in history would read off for the sample rate for instance this sensor for dual temp 2-0 1 is currently not being logged in history so would not be possible to view history for this case let’s take an overview of the miscellaneous screen which contains many useful functions calculations are used to make decisions or copy sensors conversion factors can be used to build sensor types not already included in the a K 255 alarms gives you a link to setting miscellaneous alarms the user screen can be used to display a list of important inputs or outputs on one screen the service menu allows you to offset miscellaneous sensors and override miscellaneous relay outputs or on/off inputs the status for the miscellaneous menu can be viewed through any of these points for instance if we wanted to view the status of any relay outputs programmed through the miscellaneous menu we would highlight this option as you can see no miscellaneous relay outputs are programmed if we wanted to make changes in the miscellaneous menu we would have to first select configuration calculations can be used to copy sensors calculations can be very simple or more complex depending on your needs here you see we have two calculations previously we looked at the floating calculation this calculation finds the average of four board points units is used to define the output of the calculation because we want the average of four sensors and we know that average will be in degrees Fahrenheit the units is set to si meaning sensor input degrees Fahrenheit style allows you to define what the calculation will be doing an optional description can be programmed here as you can see four sensors are listed and the average is found for the calculation to be effective the result must be correct and the current value will be reflected here let’s take a look at another calculation here you see a calculation for global phase loss this phase loss looks at two inputs if either input switches to the on value the phase loss will become true and be used in other parts of the 255 for important safety features in this case the calculation is programmed so that on/off input 1 or on/off input to be coming on will result in a current value switching to on the true line is used to tell the calculation what to do if neither input is on in this case the calculation will be off another way of looking at the word true is to think of it as the word else which is used in many plc programming strategies conversion factors can be used to set sensor types not already available in the 255 in this case you see a liquid level was utilized that did not already exist in the 255 controller the Installer knew that the

minimum input for this liquid level transducer would be 0.5 volts DC and the maximum output would be 4.0 volts DC corresponding with 0% or 100% this liquid level name was defined and then selected out of the sensor type list in the rack let’s say we wanted to create a calculation in this case the simplest calculation which would be a sensor clone because we’re in the status screen it’s not possible to create a calculation here so returning to the miscellaneous menu select configuration next calculations now you see it’s available to create a new calculation which will be defined as calculation number three let’s say we wanted to create clone which is the easiest calculation based on the outdoor air temperature we would simply need to scroll to the outdoor temps in sir based on a list of all sensor inputs the calculation will go through a startup process then display the results to clean the calculation and delete other lines not needed it’s possible to select delete for any lines left empty at this point it will go through a startup process again and give us the finished result because this calculation is not needed and just for demonstration purposes it can be deleted from the screen as well you next we’ll talk about communications options these include host communication which is defined as communication between 255 controllers IO network communication used to read inputs and control outputs other nodes that are connected to the controller rescanning and IO network overview let’s start with communications as we said host network is a list of other controllers connected on the 255 Network these can be connected through a 2 wire rs-485 network or Ethernet as you can see there are a total of 3 units on this network and all three are currently online unit 0 unit 1 and unit 2 unit 0 is defined as the master controller next the i/o network lists points is used to list points are signed this nodes will list all the boards assigned and their status overview will give us more details about individual boards including a k2 communication modules and duplicates will list any duplicate nodes on the network this is typically used during commissioning and installation rescan channels gives us the option to re-establish communication to existing boards or bring new boards online with the a.k 255 let’s take a look at this points here you see a list of all points in order by board point we know they’re in order by board point because the sort function is turned on currently we’re looking at relay outputs but we could switch to sensor inputs on off inputs variable outputs or other controllers which could include rooftop controllers such as RT C’s list nodes will list the status of boards online on this 255 as you can see all boards are currently online overview can be very useful if you’re having trouble keeping boards online or troubleshooting as you can see

there’s a button on the right that allows you to get more details on a k2 communication modules shown here here we see three communication modules those IDs are 1 2 & 3 the screen shows communication module number one has four boards number two has six boards and number three has one board the okay status means that communication is active and no boards are lost we can go one level deeper on any of these communication modules by selecting the address and pressing enter here you see important information about each board including the type of board whether it’s configured in the 255 whether 255 can see that it’s installed and any problems on the board the supply voltage refers to the voltage used to power the comm module and we can vary from the actual voltage this column shows us that the regulated 12 volt supply is a good voltage level in similar fashion the five volt supply is listed here this temperature is a temperature recorded from the board itself based on a small thermocouple incorporated into the board it will commonly run slightly higher than ambient temperatures all indications are that kamek communication module number two it working correctly if we back up to the i/o network status screen we have the option to rescan channels this would be done to bring boards online initially or to re-establish communications with boards that may have gone offline for most sites the only selection that needs to be made on this screen at the top will be channel on works this is based on the type of i/o boards that are installed if you wanted to read and scan the network we would select the rescan Network option at the bottom and press 1 or 2 if we chose one the top of the screen would give us status feedback on the operation a typical rescan will be completed in less than one minute and you’ll be giving a summary at the end of the rescan several general items are available in the store info screen such as store name the clock for this unit operating hours which are store hours any holiday schedules daylight savings dates which can be changed but should be left at the factory defaults any leak detector setups notes about contact info managers override which typically will override lighting loads and options to change units for measure languages and other preferences you