I am new in node red, i am facing problem when addition two values . how to use function block for addition?

[
    {
        "id": "ccc1360c184b413a",
        "type": "tab",
        "label": "Flow 5",
        "disabled": false,
        "info": ""
    },
    {
        "id": "27e7326f70e90168",
        "type": "modbus-read",
        "z": "ccc1360c184b413a",
        "name": "CT_5",
        "topic": "",
        "showStatusActivities": false,
        "logIOActivities": false,
        "showErrors": false,
        "unitid": "1",
        "dataType": "HoldingRegister",
        "adr": "100",
        "quantity": "60",
        "rate": "1",
        "rateUnit": "s",
        "delayOnStart": false,
        "startDelayTime": "",
        "server": "dc095a4c1ca3d0be",
        "useIOFile": false,
        "ioFile": "",
        "useIOForPayload": false,
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        "type": "function",
        "z": "ccc1360c184b413a",
        "name": "",
        "func": "msg.payload = [msg.payload[4],msg.payload[3]];\nlet pay = msg.payload;\n\nconst buf = Buffer.allocUnsafe(4);\nbuf.writeUInt16BE(pay[0],2);\nbuf.writeUInt16BE(pay[1],0);\n\nmsg.payload = buf.readFloatBE(0).toFixed(2);\nreturn msg;",
        "outputs": 1,
        "noerr": 0,
        "initialize": "",
        "finalize": "",
        "libs": [],
        "x": 440,
        "y": 160,
        "wires": [
            [
                "b8a8b938b055144f",
                "4b59511b9bd61ba9"
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    },
    {
        "id": "c3b18d970f8f2680",
        "type": "modbus-read",
        "z": "ccc1360c184b413a",
        "name": "CT_4",
        "topic": "",
        "showStatusActivities": false,
        "logIOActivities": false,
        "showErrors": false,
        "unitid": "1",
        "dataType": "HoldingRegister",
        "adr": "100",
        "quantity": "60",
        "rate": "1",
        "rateUnit": "s",
        "delayOnStart": false,
        "startDelayTime": "",
        "server": "2692a71fc2f3a35f",
        "useIOFile": false,
        "ioFile": "",
        "useIOForPayload": false,
        "emptyMsgOnFail": false,
        "x": 210,
        "y": 320,
        "wires": [
            [
                "2ada03208d088f9f"
            ],
            []
        ]
    },
    {
        "id": "2ada03208d088f9f",
        "type": "function",
        "z": "ccc1360c184b413a",
        "name": "",
        "func": "msg.payload = [msg.payload[4],msg.payload[3]];\nlet pay = msg.payload;\n\nconst buf = Buffer.allocUnsafe(4);\nbuf.writeUInt16BE(pay[0],2);\nbuf.writeUInt16BE(pay[1],0);\n\nmsg.payload = buf.readFloatBE(0).toFixed(2);\nreturn msg;",
        "outputs": 1,
        "noerr": 0,
        "initialize": "",
        "finalize": "",
        "libs": [],
        "x": 400,
        "y": 320,
        "wires": [
            [
                "6f58c147eaff54f5",
                "4b59511b9bd61ba9"
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    {
        "id": "b8a8b938b055144f",
        "type": "debug",
        "z": "ccc1360c184b413a",
        "name": "",
        "active": true,
        "tosidebar": true,
        "console": false,
        "tostatus": true,
        "complete": "payload",
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        "console": false,
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        "complete": "payload",
        "targetType": "msg",
        "statusVal": "payload",
        "statusType": "auto",
        "x": 750,
        "y": 320,
        "wires": []
    },
    {
        "id": "4b59511b9bd61ba9",
        "type": "join",
        "z": "ccc1360c184b413a",
        "name": "",
        "mode": "custom",
        "build": "array",
        "property": "payload",
        "propertyType": "msg",
        "key": "topic",
        "joiner": "\\n",
        "joinerType": "str",
        "accumulate": false,
        "timeout": "",
        "count": "2",
        "reduceRight": false,
        "reduceExp": "",
        "reduceInit": "",
        "reduceInitType": "",
        "reduceFixup": "",
        "x": 480,
        "y": 520,
        "wires": [
            [
                "c141588faab3021b",
                "250b15f56d4ccbbd"
            ]
        ]
    },
    {
        "id": "c141588faab3021b",
        "type": "debug",
        "z": "ccc1360c184b413a",
        "name": "",
        "active": true,
        "tosidebar": true,
        "console": false,
        "tostatus": true,
        "complete": "payload",
        "targetType": "msg",
        "statusVal": "payload",
        "statusType": "auto",
        "x": 730,
        "y": 400,
        "wires": []
    },
    {
        "id": "8e9d7ef5c3fcdf2a",
        "type": "debug",
        "z": "ccc1360c184b413a",
        "name": "",
        "active": true,
        "tosidebar": true,
        "console": true,
        "tostatus": true,
        "complete": "payload",
        "targetType": "msg",
        "statusVal": "payload",
        "statusType": "auto",
        "x": 940,
        "y": 520,
        "wires": []
    },
    {
        "id": "250b15f56d4ccbbd",
        "type": "change",
        "z": "ccc1360c184b413a",
        "name": "",
        "rules": [
            {
                "t": "set",
                "p": "payload",
                "pt": "msg",
                "to": "$sum(array)\t",
                "tot": "jsonata"
            }
        ],
        "action": "",
        "property": "",
        "from": "",
        "to": "",
        "reg": false,
        "x": 700,
        "y": 520,
        "wires": [
            [
                "8e9d7ef5c3fcdf2a"
            ]
        ]
    },
    {
        "id": "dc095a4c1ca3d0be",
        "type": "modbus-client",
        "name": "LOCATION_5",
        "clienttype": "tcp",
        "bufferCommands": true,
        "stateLogEnabled": false,
        "queueLogEnabled": false,
        "tcpHost": "103.62.95.123",
        "tcpPort": "502",
        "tcpType": "DEFAULT",
        "serialPort": "/dev/ttyUSB",
        "serialType": "RTU-BUFFERD",
        "serialBaudrate": "9600",
        "serialDatabits": "8",
        "serialStopbits": "1",
        "serialParity": "none",
        "serialConnectionDelay": "100",
        "serialAsciiResponseStartDelimiter": "",
        "unit_id": "1",
        "commandDelay": "1",
        "clientTimeout": "1000",
        "reconnectOnTimeout": true,
        "reconnectTimeout": "2000",
        "parallelUnitIdsAllowed": false
    },
    {
        "id": "2692a71fc2f3a35f",
        "type": "modbus-client",
        "name": "LOCATION_4",
        "clienttype": "tcp",
        "bufferCommands": true,
        "stateLogEnabled": false,
        "queueLogEnabled": false,
        "tcpHost": "103.62.95.145",
        "tcpPort": "502",
        "tcpType": "DEFAULT",
        "serialPort": "/dev/ttyUSB",
        "serialType": "RTU-BUFFERD",
        "serialBaudrate": "9600",
        "serialDatabits": "8",
        "serialStopbits": "1",
        "serialParity": "none",
        "serialConnectionDelay": "100",
        "serialAsciiResponseStartDelimiter": "",
        "unit_id": 1,
        "commandDelay": 1,
        "clientTimeout": 1000,
        "reconnectOnTimeout": true,
        "reconnectTimeout": 2000,
        "parallelUnitIdsAllowed": false
    }
]

You may need to include just a bit more information on what you are wanting to do.

All I see is a message contents displayed. (Guessing)
But not what you are trying to add.

Ok sorry.

But maybe a walk through to help people understand what you are doing.

What are you seeing in the debug nodes?
Using foreign nodes in your examples is not helpful as others may not have those nodes.

Rather it would be better to make dummy nodes (inject and change) to construct the message/s you are receiving and then others can see what it is you are getting.

P.S.

It would seem you are adding the values in the change node: it won't work.
All variables are valid only at the time of them being sent.
If you want to add the value of one input to the value of another (which you haven't really explained) the second set of values won't exist.

But again:
You haven't explained enough what it is and what you are seeing.

Please put in the nodes as suggested above with the inject and change to make the messages and repost the code.

[
    {
        "id": "ccc1360c184b413a",
        "type": "tab",
        "label": "Flow 5",
        "disabled": false,
        "info": ""
    },
    {
        "id": "27e7326f70e90168",
        "type": "modbus-read",
        "z": "ccc1360c184b413a",
        "name": "CT_5",
        "topic": "",
        "showStatusActivities": false,
        "logIOActivities": false,
        "showErrors": false,
        "unitid": "1",
        "dataType": "HoldingRegister",
        "adr": "100",
        "quantity": "60",
        "rate": "1",
        "rateUnit": "s",
        "delayOnStart": false,
        "startDelayTime": "",
        "server": "dc095a4c1ca3d0be",
        "useIOFile": false,
        "ioFile": "",
        "useIOForPayload": false,
        "emptyMsgOnFail": false,
        "x": 210,
        "y": 160,
        "wires": [
            [
                "d3c328a720ac9183"
            ],
            []
        ]
    },
    {
        "id": "d3c328a720ac9183",
        "type": "function",
        "z": "ccc1360c184b413a",
        "name": "",
        "func": "msg.payload = [msg.payload[4],msg.payload[3]];\nlet pay = msg.payload;\n\nconst buf = Buffer.allocUnsafe(4);\nbuf.writeUInt16BE(pay[0],2);\nbuf.writeUInt16BE(pay[1],0);\n\nmsg.payload = buf.readFloatBE(0).toFixed(2);\nreturn msg;",
        "outputs": 1,
        "noerr": 0,
        "initialize": "",
        "finalize": "",
        "libs": [],
        "x": 440,
        "y": 160,
        "wires": [
            [
                "812cfffb8fad5391"
            ]
        ]
    },
    {
        "id": "c3b18d970f8f2680",
        "type": "modbus-read",
        "z": "ccc1360c184b413a",
        "name": "CT_4",
        "topic": "",
        "showStatusActivities": false,
        "logIOActivities": false,
        "showErrors": false,
        "unitid": "1",
        "dataType": "HoldingRegister",
        "adr": "100",
        "quantity": "60",
        "rate": "1",
        "rateUnit": "s",
        "delayOnStart": false,
        "startDelayTime": "",
        "server": "2692a71fc2f3a35f",
        "useIOFile": false,
        "ioFile": "",
        "useIOForPayload": false,
        "emptyMsgOnFail": false,
        "x": 210,
        "y": 320,
        "wires": [
            [
                "2ada03208d088f9f"
            ],
            []
        ]
    },
    {
        "id": "2ada03208d088f9f",
        "type": "function",
        "z": "ccc1360c184b413a",
        "name": "",
        "func": "msg.payload = [msg.payload[4],msg.payload[3]];\nlet pay = msg.payload;\n\nconst buf = Buffer.allocUnsafe(4);\nbuf.writeUInt16BE(pay[0],2);\nbuf.writeUInt16BE(pay[1],0);\n\nmsg.payload = buf.readFloatBE(0).toFixed(2);\nreturn msg;",
        "outputs": 1,
        "noerr": 0,
        "initialize": "",
        "finalize": "",
        "libs": [],
        "x": 400,
        "y": 320,
        "wires": [
            [
                "de59d139359235a0"
            ]
        ]
    },
    {
        "id": "812cfffb8fad5391",
        "type": "change",
        "z": "ccc1360c184b413a",
        "name": "",
        "rules": [
            {
                "t": "set",
                "p": "v1",
                "pt": "flow",
                "to": "payload",
                "tot": "msg"
            }
        ],
        "action": "",
        "property": "",
        "from": "",
        "to": "",
        "reg": false,
        "x": 575,
        "y": 77,
        "wires": [
            [
                "0ea204ed95afb028"
            ]
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    },
    {
        "id": "de59d139359235a0",
        "type": "change",
        "z": "ccc1360c184b413a",
        "name": "",
        "rules": [
            {
                "t": "set",
                "p": "v2",
                "pt": "flow",
                "to": "payload",
                "tot": "msg"
            }
        ],
        "action": "",
        "property": "",
        "from": "",
        "to": "",
        "reg": false,
        "x": 510,
        "y": 240,
        "wires": [
            [
                "0ea204ed95afb028"
            ]
        ]
    },
    {
        "id": "0ea204ed95afb028",
        "type": "change",
        "z": "ccc1360c184b413a",
        "name": "sum",
        "rules": [
            {
                "t": "set",
                "p": "payload",
                "pt": "msg",
                "to": "$number($flowContext('v1')) + $number($flowContext('v2')) + $number($flowContext('v3'))",
                "tot": "jsonata"
            }
        ],
        "action": "",
        "property": "",
        "from": "",
        "to": "",
        "reg": false,
        "x": 728,
        "y": 180,
        "wires": [
            [
                "aa3809a6d2a20046"
            ]
        ]
    },
    {
        "id": "9377623d8ccca450",
        "type": "modbus-read",
        "z": "ccc1360c184b413a",
        "name": "AIRPORT",
        "topic": "",
        "showStatusActivities": false,
        "logIOActivities": false,
        "showErrors": false,
        "unitid": "1",
        "dataType": "HoldingRegister",
        "adr": "100",
        "quantity": "60",
        "rate": "1",
        "rateUnit": "s",
        "delayOnStart": false,
        "startDelayTime": "",
        "server": "6b455b808110be31",
        "useIOFile": false,
        "ioFile": "",
        "useIOForPayload": false,
        "emptyMsgOnFail": false,
        "x": 160,
        "y": 460,
        "wires": [
            [
                "25681a0bc899f589"
            ],
            []
        ]
    },
    {
        "id": "25681a0bc899f589",
        "type": "function",
        "z": "ccc1360c184b413a",
        "name": "",
        "func": "msg.payload = [msg.payload[4],msg.payload[3]];\nlet pay = msg.payload;\n\nconst buf = Buffer.allocUnsafe(4);\nbuf.writeUInt16BE(pay[0],2);\nbuf.writeUInt16BE(pay[1],0);\n\nmsg.payload = buf.readFloatBE(0).toFixed(2);\nreturn msg;",
        "outputs": 1,
        "noerr": 0,
        "initialize": "",
        "finalize": "",
        "libs": [],
        "x": 380,
        "y": 460,
        "wires": [
            [
                "17a6979a6d639802"
            ]
        ]
    },
    {
        "id": "17a6979a6d639802",
        "type": "change",
        "z": "ccc1360c184b413a",
        "name": "",
        "rules": [
            {
                "t": "set",
                "p": "v3",
                "pt": "flow",
                "to": "payload",
                "tot": "msg"
            }
        ],
        "action": "",
        "property": "",
        "from": "",
        "to": "",
        "reg": false,
        "x": 597,
        "y": 378,
        "wires": [
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                "0ea204ed95afb028",
                "51aff0b66a93d412"
            ]
        ]
    },
    {
        "id": "51aff0b66a93d412",
        "type": "debug",
        "z": "ccc1360c184b413a",
        "name": "",
        "active": true,
        "tosidebar": true,
        "console": false,
        "tostatus": true,
        "complete": "payload",
        "targetType": "msg",
        "statusVal": "payload",
        "statusType": "auto",
        "x": 831,
        "y": 400,
        "wires": []
    },
    {
        "id": "aa3809a6d2a20046",
        "type": "debug",
        "z": "ccc1360c184b413a",
        "name": "",
        "active": true,
        "tosidebar": true,
        "console": false,
        "tostatus": true,
        "complete": "payload",
        "targetType": "msg",
        "statusVal": "payload",
        "statusType": "auto",
        "x": 897,
        "y": 281,
        "wires": []
    },
    {
        "id": "dc095a4c1ca3d0be",
        "type": "modbus-client",
        "name": "LOCATION_5",
        "clienttype": "tcp",
        "bufferCommands": true,
        "stateLogEnabled": false,
        "queueLogEnabled": false,
        "tcpHost": "103.62.95.123",
        "tcpPort": "502",
        "tcpType": "DEFAULT",
        "serialPort": "/dev/ttyUSB",
        "serialType": "RTU-BUFFERD",
        "serialBaudrate": "9600",
        "serialDatabits": "8",
        "serialStopbits": "1",
        "serialParity": "none",
        "serialConnectionDelay": "100",
        "serialAsciiResponseStartDelimiter": "",
        "unit_id": "1",
        "commandDelay": "1",
        "clientTimeout": "1000",
        "reconnectOnTimeout": true,
        "reconnectTimeout": "2000",
        "parallelUnitIdsAllowed": false
    },
    {
        "id": "2692a71fc2f3a35f",
        "type": "modbus-client",
        "name": "LOCATION_4",
        "clienttype": "tcp",
        "bufferCommands": true,
        "stateLogEnabled": false,
        "queueLogEnabled": false,
        "tcpHost": "103.62.95.145",
        "tcpPort": "502",
        "tcpType": "DEFAULT",
        "serialPort": "/dev/ttyUSB",
        "serialType": "RTU-BUFFERD",
        "serialBaudrate": "9600",
        "serialDatabits": "8",
        "serialStopbits": "1",
        "serialParity": "none",
        "serialConnectionDelay": "100",
        "serialAsciiResponseStartDelimiter": "",
        "unit_id": 1,
        "commandDelay": 1,
        "clientTimeout": 1000,
        "reconnectOnTimeout": true,
        "reconnectTimeout": 2000,
        "parallelUnitIdsAllowed": false
    },
    {
        "id": "6b455b808110be31",
        "type": "modbus-client",
        "name": "AIRPORT",
        "clienttype": "tcp",
        "bufferCommands": true,
        "stateLogEnabled": false,
        "queueLogEnabled": false,
        "tcpHost": "103.62.95.133",
        "tcpPort": "502",
        "tcpType": "DEFAULT",
        "serialPort": "/dev/ttyUSB",
        "serialType": "RTU-BUFFERD",
        "serialBaudrate": "9600",
        "serialDatabits": "8",
        "serialStopbits": "1",
        "serialParity": "none",
        "serialConnectionDelay": "100",
        "serialAsciiResponseStartDelimiter": "",
        "unit_id": "1",
        "commandDelay": "1",
        "clientTimeout": "1000",
        "reconnectOnTimeout": true,
        "reconnectTimeout": "2000",
        "parallelUnitIdsAllowed": false
    }
][quote="Trying_to_learn, post:2, topic:62348, full:true"]
You may need to include just a bit more information on what you are wanting to do.

~~All I see is a message contents displayed.  (Guessing)~~
~~But not what you are trying to add.~~

Ok sorry.

But maybe a *walk through* to help people understand what you are doing.

What are you seeing in the `debug` nodes?
Using *foreign* nodes in your examples is not helpful as others may not have those nodes.

Rather it would be better to make *dummy* nodes (`inject` and `change`) to construct the message/s you are receiving and then others can see what it is you are getting.

P.S.

It would seem you are adding the values in the `change` node:  it won't work.
All variables are valid only at the time of them being sent.
If you want to add the value of one input to the value of another (which you haven't really explained) the second set of values won't exist.

But again:
You haven't explained enough what it is and what you are seeing.

Please put in the nodes as suggested above with the `inject` and `change` to make the messages and repost the code.
[/quote]

actually i am using three different IP Modbus values addition but unfortunately when any one data is not coming then its showing error message. 

[quote="jitesh, post:3, topic:62348, full:true"]

[
    {
        "id": "ccc1360c184b413a",
        "type": "tab",
        "label": "Flow 5",
        "disabled": false,
        "info": ""
    },
    {
        "id": "27e7326f70e90168",
        "type": "modbus-read",
        "z": "ccc1360c184b413a",
        "name": "CT_5",
        "topic": "",
        "showStatusActivities": false,
        "logIOActivities": false,
        "showErrors": false,
        "unitid": "1",
        "dataType": "HoldingRegister",
        "adr": "100",
        "quantity": "60",
        "rate": "1",
        "rateUnit": "s",
        "delayOnStart": false,
        "startDelayTime": "",
        "server": "dc095a4c1ca3d0be",
        "useIOFile": false,
        "ioFile": "",
        "useIOForPayload": false,
        "emptyMsgOnFail": false,
        "x": 210,
        "y": 160,
        "wires": [
            [
                "d3c328a720ac9183"
            ],
            []
        ]
    },
    {
        "id": "d3c328a720ac9183",
        "type": "function",
        "z": "ccc1360c184b413a",
        "name": "",
        "func": "msg.payload = [msg.payload[4],msg.payload[3]];\nlet pay = msg.payload;\n\nconst buf = Buffer.allocUnsafe(4);\nbuf.writeUInt16BE(pay[0],2);\nbuf.writeUInt16BE(pay[1],0);\n\nmsg.payload = buf.readFloatBE(0).toFixed(2);\nreturn msg;",
        "outputs": 1,
        "noerr": 0,
        "initialize": "",
        "finalize": "",
        "libs": [],
        "x": 440,
        "y": 160,
        "wires": [
            [
                "812cfffb8fad5391"
            ]
        ]
    },
    {
        "id": "c3b18d970f8f2680",
        "type": "modbus-read",
        "z": "ccc1360c184b413a",
        "name": "CT_4",
        "topic": "",
        "showStatusActivities": false,
        "logIOActivities": false,
        "showErrors": false,
        "unitid": "1",
        "dataType": "HoldingRegister",
        "adr": "100",
        "quantity": "60",
        "rate": "1",
        "rateUnit": "s",
        "delayOnStart": false,
        "startDelayTime": "",
        "server": "2692a71fc2f3a35f",
        "useIOFile": false,
        "ioFile": "",
        "useIOForPayload": false,
        "emptyMsgOnFail": false,
        "x": 210,
        "y": 320,
        "wires": [
            [
                "2ada03208d088f9f"
            ],
            []
        ]
    },
    {
        "id": "2ada03208d088f9f",
        "type": "function",
        "z": "ccc1360c184b413a",
        "name": "",
        "func": "msg.payload = [msg.payload[4],msg.payload[3]];\nlet pay = msg.payload;\n\nconst buf = Buffer.allocUnsafe(4);\nbuf.writeUInt16BE(pay[0],2);\nbuf.writeUInt16BE(pay[1],0);\n\nmsg.payload = buf.readFloatBE(0).toFixed(2);\nreturn msg;",
        "outputs": 1,
        "noerr": 0,
        "initialize": "",
        "finalize": "",
        "libs": [],
        "x": 400,
        "y": 320,
        "wires": [
            [
                "de59d139359235a0"
            ]
        ]
    },
    {
        "id": "812cfffb8fad5391",
        "type": "change",
        "z": "ccc1360c184b413a",
        "name": "",
        "rules": [
            {
                "t": "set",
                "p": "v1",
                "pt": "flow",
                "to": "payload",
                "tot": "msg"
            }
        ],
        "action": "",
        "property": "",
        "from": "",
        "to": "",
        "reg": false,
        "x": 575,
        "y": 77,
        "wires": [
            [
                "0ea204ed95afb028"
            ]
        ]
    },
    {
        "id": "de59d139359235a0",
        "type": "change",
        "z": "ccc1360c184b413a",
        "name": "",
        "rules": [
            {
                "t": "set",
                "p": "v2",
                "pt": "flow",
                "to": "payload",
                "tot": "msg"
            }
        ],
        "action": "",
        "property": "",
        "from": "",
        "to": "",
        "reg": false,
        "x": 510,
        "y": 240,
        "wires": [
            [
                "0ea204ed95afb028"
            ]
        ]
    },
    {
        "id": "0ea204ed95afb028",
        "type": "change",
        "z": "ccc1360c184b413a",
        "name": "sum",
        "rules": [
            {
                "t": "set",
                "p": "payload",
                "pt": "msg",
                "to": "$number($flowContext('v1')) + $number($flowContext('v2')) + $number($flowContext('v3'))",
                "tot": "jsonata"
            }
        ],
        "action": "",
        "property": "",
        "from": "",
        "to": "",
        "reg": false,
        "x": 728,
        "y": 180,
        "wires": [
            [
                "aa3809a6d2a20046"
            ]
        ]
    },
    {
        "id": "9377623d8ccca450",
        "type": "modbus-read",
        "z": "ccc1360c184b413a",
        "name": "AIRPORT",
        "topic": "",
        "showStatusActivities": false,
        "logIOActivities": false,
        "showErrors": false,
        "unitid": "1",
        "dataType": "HoldingRegister",
        "adr": "100",
        "quantity": "60",
        "rate": "1",
        "rateUnit": "s",
        "delayOnStart": false,
        "startDelayTime": "",
        "server": "6b455b808110be31",
        "useIOFile": false,
        "ioFile": "",
        "useIOForPayload": false,
        "emptyMsgOnFail": false,
        "x": 160,
        "y": 460,
        "wires": [
            [
                "25681a0bc899f589"
            ],
            []
        ]
    },
    {
        "id": "25681a0bc899f589",
        "type": "function",
        "z": "ccc1360c184b413a",
        "name": "",
        "func": "msg.payload = [msg.payload[4],msg.payload[3]];\nlet pay = msg.payload;\n\nconst buf = Buffer.allocUnsafe(4);\nbuf.writeUInt16BE(pay[0],2);\nbuf.writeUInt16BE(pay[1],0);\n\nmsg.payload = buf.readFloatBE(0).toFixed(2);\nreturn msg;",
        "outputs": 1,
        "noerr": 0,
        "initialize": "",
        "finalize": "",
        "libs": [],
        "x": 380,
        "y": 460,
        "wires": [
            [
                "17a6979a6d639802"
            ]
        ]
    },
    {
        "id": "17a6979a6d639802",
        "type": "change",
        "z": "ccc1360c184b413a",
        "name": "",
        "rules": [
            {
                "t": "set",
                "p": "v3",
                "pt": "flow",
                "to": "payload",
                "tot": "msg"
            }
        ],
        "action": "",
        "property": "",
        "from": "",
        "to": "",
        "reg": false,
        "x": 597,
        "y": 378,
        "wires": [
            [
                "0ea204ed95afb028",
                "51aff0b66a93d412"
            ]
        ]
    },
    {
        "id": "51aff0b66a93d412",
        "type": "debug",
        "z": "ccc1360c184b413a",
        "name": "",
        "active": true,
        "tosidebar": true,
        "console": false,
        "tostatus": true,
        "complete": "payload",
        "targetType": "msg",
        "statusVal": "payload",
        "statusType": "auto",
        "x": 831,
        "y": 400,
        "wires": []
    },
    {
        "id": "aa3809a6d2a20046",
        "type": "debug",
        "z": "ccc1360c184b413a",
        "name": "",
        "active": true,
        "tosidebar": true,
        "console": false,
        "tostatus": true,
        "complete": "payload",
        "targetType": "msg",
        "statusVal": "payload",
        "statusType": "auto",
        "x": 897,
        "y": 281,
        "wires": []
    },
    {
        "id": "dc095a4c1ca3d0be",
        "type": "modbus-client",
        "name": "LOCATION_5",
        "clienttype": "tcp",
        "bufferCommands": true,
        "stateLogEnabled": false,
        "queueLogEnabled": false,
        "tcpHost": "103.62.95.123",
        "tcpPort": "502",
        "tcpType": "DEFAULT",
        "serialPort": "/dev/ttyUSB",
        "serialType": "RTU-BUFFERD",
        "serialBaudrate": "9600",
        "serialDatabits": "8",
        "serialStopbits": "1",
        "serialParity": "none",
        "serialConnectionDelay": "100",
        "serialAsciiResponseStartDelimiter": "",
        "unit_id": "1",
        "commandDelay": "1",
        "clientTimeout": "1000",
        "reconnectOnTimeout": true,
        "reconnectTimeout": "2000",
        "parallelUnitIdsAllowed": false
    },
    {
        "id": "2692a71fc2f3a35f",
        "type": "modbus-client",
        "name": "LOCATION_4",
        "clienttype": "tcp",
        "bufferCommands": true,
        "stateLogEnabled": false,
        "queueLogEnabled": false,
        "tcpHost": "103.62.95.145",
        "tcpPort": "502",
        "tcpType": "DEFAULT",
        "serialPort": "/dev/ttyUSB",
        "serialType": "RTU-BUFFERD",
        "serialBaudrate": "9600",
        "serialDatabits": "8",
        "serialStopbits": "1",
        "serialParity": "none",
        "serialConnectionDelay": "100",
        "serialAsciiResponseStartDelimiter": "",
        "unit_id": 1,
        "commandDelay": 1,
        "clientTimeout": 1000,
        "reconnectOnTimeout": true,
        "reconnectTimeout": 2000,
        "parallelUnitIdsAllowed": false
    },
    {
        "id": "6b455b808110be31",
        "type": "modbus-client",
        "name": "AIRPORT",
        "clienttype": "tcp",
        "bufferCommands": true,
        "stateLogEnabled": false,
        "queueLogEnabled": false,
        "tcpHost": "103.62.95.133",
        "tcpPort": "502",
        "tcpType": "DEFAULT",
        "serialPort": "/dev/ttyUSB",
        "serialType": "RTU-BUFFERD",
        "serialBaudrate": "9600",
        "serialDatabits": "8",
        "serialStopbits": "1",
        "serialParity": "none",
        "serialConnectionDelay": "100",
        "serialAsciiResponseStartDelimiter": "",
        "unit_id": "1",
        "commandDelay": "1",
        "clientTimeout": "1000",
        "reconnectOnTimeout": true,
        "reconnectTimeout": "2000",
        "parallelUnitIdsAllowed": false
    }
]

actually i am using three different IP Modbus values addition but unfortunately when any one data is not coming then its showing error message.

please check the image also

What is this? I can't import it.

And what are those orange nodes at the left of the flow?

CT-5 CT-4 AIRPORT

It looks like they are Modbus nodes.
Modbus
Screen Shot 05-08-22 at 07.49 AM

Your third modbus does not have any value - that's why you get undefined.

If you use a function node you can check before adding.

Alternatively, you can avoid using context altogether and use a join node set for a count of 3.

But.... (Playing devil's advocate)

If all three (different) messages get out of sync: it will play havoc on the output value.

Sorry... But it could happen.

Since the op is simply adding, it doesn't matter what order the values come in. However, to avoid that never use array mode. Instead, use the key value mode and the variables no matter what order they arrive will always be in the same key.

Sorry.. Really. Sorry.

Sir please share any example when 3 data will add and one of them showing undefined value.
please sir........thanks in advance

Sir please share any example when 3 data will add and one of them showing undefined value.
please sir........thanks in advance[quote="jitesh, post:1, topic:62348, full:true"]

[
    {
        "id": "ccc1360c184b413a",
        "type": "tab",
        "label": "Flow 5",
        "disabled": false,
        "info": ""
    },
    {
        "id": "27e7326f70e90168",
        "type": "modbus-read",
        "z": "ccc1360c184b413a",
        "name": "CT_5",
        "topic": "",
        "showStatusActivities": false,
        "logIOActivities": false,
        "showErrors": false,
        "unitid": "1",
        "dataType": "HoldingRegister",
        "adr": "100",
        "quantity": "60",
        "rate": "1",
        "rateUnit": "s",
        "delayOnStart": false,
        "startDelayTime": "",
        "server": "dc095a4c1ca3d0be",
        "useIOFile": false,
        "ioFile": "",
        "useIOForPayload": false,
        "emptyMsgOnFail": false,
        "x": 210,
        "y": 160,
        "wires": [
            [
                "d3c328a720ac9183"
            ],
            []
        ]
    },
    {
        "id": "d3c328a720ac9183",
        "type": "function",
        "z": "ccc1360c184b413a",
        "name": "",
        "func": "msg.payload = [msg.payload[4],msg.payload[3]];\nlet pay = msg.payload;\n\nconst buf = Buffer.allocUnsafe(4);\nbuf.writeUInt16BE(pay[0],2);\nbuf.writeUInt16BE(pay[1],0);\n\nmsg.payload = buf.readFloatBE(0).toFixed(2);\nreturn msg;",
        "outputs": 1,
        "noerr": 0,
        "initialize": "",
        "finalize": "",
        "libs": [],
        "x": 440,
        "y": 160,
        "wires": [
            [
                "b8a8b938b055144f",
                "4b59511b9bd61ba9"
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    },
    {
        "id": "c3b18d970f8f2680",
        "type": "modbus-read",
        "z": "ccc1360c184b413a",
        "name": "CT_4",
        "topic": "",
        "showStatusActivities": false,
        "logIOActivities": false,
        "showErrors": false,
        "unitid": "1",
        "dataType": "HoldingRegister",
        "adr": "100",
        "quantity": "60",
        "rate": "1",
        "rateUnit": "s",
        "delayOnStart": false,
        "startDelayTime": "",
        "server": "2692a71fc2f3a35f",
        "useIOFile": false,
        "ioFile": "",
        "useIOForPayload": false,
        "emptyMsgOnFail": false,
        "x": 210,
        "y": 320,
        "wires": [
            [
                "2ada03208d088f9f"
            ],
            []
        ]
    },
    {
        "id": "2ada03208d088f9f",
        "type": "function",
        "z": "ccc1360c184b413a",
        "name": "",
        "func": "msg.payload = [msg.payload[4],msg.payload[3]];\nlet pay = msg.payload;\n\nconst buf = Buffer.allocUnsafe(4);\nbuf.writeUInt16BE(pay[0],2);\nbuf.writeUInt16BE(pay[1],0);\n\nmsg.payload = buf.readFloatBE(0).toFixed(2);\nreturn msg;",
        "outputs": 1,
        "noerr": 0,
        "initialize": "",
        "finalize": "",
        "libs": [],
        "x": 400,
        "y": 320,
        "wires": [
            [
                "6f58c147eaff54f5",
                "4b59511b9bd61ba9"
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    },
    {
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        "type": "debug",
        "z": "ccc1360c184b413a",
        "name": "",
        "active": true,
        "tosidebar": true,
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        "tostatus": true,
        "complete": "payload",
        "targetType": "msg",
        "statusVal": "payload",
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        "wires": []
    },
    {
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        "type": "debug",
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        "complete": "payload",
        "targetType": "msg",
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        "x": 750,
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        "wires": []
    },
    {
        "id": "4b59511b9bd61ba9",
        "type": "join",
        "z": "ccc1360c184b413a",
        "name": "",
        "mode": "custom",
        "build": "array",
        "property": "payload",
        "propertyType": "msg",
        "key": "topic",
        "joiner": "\\n",
        "joinerType": "str",
        "accumulate": false,
        "timeout": "",
        "count": "2",
        "reduceRight": false,
        "reduceExp": "",
        "reduceInit": "",
        "reduceInitType": "",
        "reduceFixup": "",
        "x": 480,
        "y": 520,
        "wires": [
            [
                "c141588faab3021b",
                "250b15f56d4ccbbd"
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    {
        "id": "c141588faab3021b",
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        "active": true,
        "tosidebar": true,
        "console": true,
        "tostatus": true,
        "complete": "payload",
        "targetType": "msg",
        "statusVal": "payload",
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        "y": 520,
        "wires": []
    },
    {
        "id": "250b15f56d4ccbbd",
        "type": "change",
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        "name": "",
        "rules": [
            {
                "t": "set",
                "p": "payload",
                "pt": "msg",
                "to": "$sum(array)\t",
                "tot": "jsonata"
            }
        ],
        "action": "",
        "property": "",
        "from": "",
        "to": "",
        "reg": false,
        "x": 700,
        "y": 520,
        "wires": [
            [
                "8e9d7ef5c3fcdf2a"
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        ]
    },
    {
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        "serialParity": "none",
        "serialConnectionDelay": "100",
        "serialAsciiResponseStartDelimiter": "",
        "unit_id": "1",
        "commandDelay": "1",
        "clientTimeout": "1000",
        "reconnectOnTimeout": true,
        "reconnectTimeout": "2000",
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    {
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        "serialDatabits": "8",
        "serialStopbits": "1",
        "serialParity": "none",
        "serialConnectionDelay": "100",
        "serialAsciiResponseStartDelimiter": "",
        "unit_id": 1,
        "commandDelay": 1,
        "clientTimeout": 1000,
        "reconnectOnTimeout": true,
        "reconnectTimeout": 2000,
        "parallelUnitIdsAllowed": false
    }
]

[/quote]