How to migrate a Nexus 1250 with I/O modules to a Nexus 1450

Replacing a Nexus 1250 meter with external modules by a Nexus 1450 while keeping signals, addresses and wiring: what to extract beforehand, what changes in the communications and how to carry the analogue scaling across.

Summary. The Electro Industries/GaugeTech Nexus 1450 is the natural successor to the Nexus 1250/1252 once support for the older platform runs out or real Ethernet, DNP3 over TCP, IEC 61850 or SNTP is required. For anyone migrating, the good news is that the serial side, the I/O module bus and the Communicator profile format carry over almost one to one; the network side changes completely. This article walks through the process on a typical case: a 1250 with one 4PO1 pulse-output module and four 20mAON4 analogue-output modules, replaced by a 1450 with the same set of modules.

1. What stays and what changes

What stays:

• Four independent, isolated serial ports (Port 1 switchable RS232/RS485, Ports 2–4 RS485), with the same address, baud rate, format and protocol table.
• The same external I/O modules (1mAON4/8, 20mAON4/8, 8AI1–4, 4RO1, 4PO1, 8DI1), with the same factory Modbus addresses, hung off a port in Master (I/O Modules) mode at 57600 baud.
• The Communicator EXT / CommunicatorPQA device profile, which lets you copy CT/PT ratios, limits, historical logs and analogue output assignments.
• The geometry. The 1450 is designed as a drop-in replacement for the 1250/1252: same enclosure, same panel cut-out and same fixings, and the same terminal layout for voltages, currents, L(+)/N(−) auxiliary supply and the four serial ports. The original panel wiring, with its terminals already crimped, is disconnected from the 1250 and connected to the 1450 on the same terminals, without pulling a single new wire. The only things that did not exist on the 1250 are the new connectors: the Port 5 RJ45, the Port 6 fibre and the IRIG-B input, which are only wired if they are going to be used.

What changes:

• The RS485 gateway of the 1250’s INP200 Ethernet option disappears. The 1450 has two native network interfaces (Port 5 RJ45 and Port 6 fibre), each with its own IP, with no meters daisy-chained behind them.
• The external display is no longer tied to Port 3; it can go on any of Ports 1–4 at 9600 baud.
• A brand-new 1450 ships at 9600 baud on all four serial ports, whereas a 1250 in the field is usually at 57600 on the PC and I/O ports.
• Ethernet ports with fixed factory IPs (10.0.0.1 on the RJ45, 10.0.1.1 on the fibre) and a PROG/FIXED switch beneath the RJ45 to recover a meter whose IP has been lost.

2. Before removing the 1250: what to take with you

The most expensive mistake in this migration is taking the 1250 out without first extracting what lives only inside it and its modules. With the meter still in service, four things need to be collected.

1. The device profile. With Communicator EXT or CommunicatorPQA, Retrieve Device Profile and save the .nps file; then Reports › Device Profile Report and save it as HTML or PDF. That captures the CT/PT ratios, the hookup (wye or delta), the full scales for limits and waveforms, the historical logs and the communications table for all four ports.
2. The module table. In Device Profile › I/O Modules, note for each module its row number, its identifier (AO Module 1, KYZ Module 1…), type, Modbus address and meter port. This is the map that will later be reproduced on the 1450.
3. The channel assignment of each module, module by module. This is the point that catches people out: for the analogue modules, the 1250’s Device Profile Report only lists Port Number and Module Address; the Assigned Channel / Scale High / Scale Low rows come out blank because that information is stored in the module itself, not in the meter. Each module has to be opened with the Edit button under Module Settings (the Analog Output 4 to 20 mA External Module Programmer dialogue) and the quantity, the value at 20 mA and the value at 4 mA copied for each channel; for the KYZ module, the quantity and pulse weight of each output. One screenshot per module is enough, and more reliable than transcribing.
4. What lies outside the meter. Which 4–20 mA loop goes to which input of the control system, which counter receives each KYZ output, the 1250’s IP if it has an INP200 and which devices hang off its RS485 gateway, and the control power suffix on the label.

In the typical case, the inventory of the 1250 looks like this:

Before touching the 1450, it is worth reading its label in the same way: a meter with option D (18–60 V DC) will not start on a 230 V AC or 125 V DC auxiliary supply, and the option cannot be changed in the field.

3. Communications: factory defaults and first link with the 1450

The first connection almost always fails because of the baud rate, not the cable. There are three sets of values that should not be confused: those EIG documents as factory defaults, those a meter already programmed in the field usually has, and those Communicator fills in on a blank profile (9600, Modbus RTU, 8-N-1), which belong to the software and say nothing about the state of the meter.

Nexus 1250/1252 (manual E107706, Communicator §2.2). From the factory: Port 1 address 1 at 57600, Port 2 at 57600, Port 3 at 9600 (external display or modules) and Port 4 at 57600; all Modbus RTU, 8-N-1, 0 ms delay. In installations that have already been programmed it is common to find the 9600 port on Port 2 and Ports 3 and 4 as I/O masters at 57600. If a port does not answer at 57600, try 9600 before declaring anything faulty. Port 1 is switchable RS232/RS485 with the selector beneath the connector; in RS232 it is DCE (female DB9, pin 2 Tx, 3 Rx, 5 GND) and supports no more than 15 m.

Nexus 1450 (manual E171701 §4 and §5, quickstart E171703). A new meter answers at 9600 on all four serial ports: Modbus RTU on RS485 and Modbus ASCII on the Port 1 RS232. Port 4 can additionally act as a generic RTU master over Modbus slaves (up to 128 registers). The two Ethernet ports ship with a fixed IP and DHCP disabled:

No bonding or teaming: if both ports are used they must be on different subnets, which is exactly what the factory defaults do.

Recommended first link: Ethernet. Set the PROG/FIXED switch beneath the RJ45 to FIXED (the meter answers at 10.0.0.1 even if another IP is stored; the port’s third LED indicates this), give the PC a manual IP on the same subnet (for example 10.0.0.10 / 255.255.255.0, no gateway), a direct Ethernet cable and ping 10.0.0.1. Opening http://10.0.0.1 in the browser brings up WebView with nothing to install: it is the quickest link test. Then, in Communicator, Connect › Network with Device Address 1, host 10.0.0.1, port 502, Modbus TCP. When finished, return the switch to PROG and put the PC back on DHCP.

First link over serial, if no Ethernet is to hand. Port 1 (RS232 on the meter itself), address 1, 8-N-1, Modbus RTU; 9600 if the unit is new, 57600 if it has already been programmed. For RS485 towards the PC use Ports 2–4 or a converter.

The I/O ports keep their baud rate. The modules ship at 57600 and the meter port that drives them must be at 57600, Modbus RTU, 8-N-1, 0 ms delay and Master (I/O Modules) mode. The configuration is the same on the 1250 and the 1450; on a new 1450 it has to be programmed, because it ships at 9600.

The gateway is gone. On a 1250 with INP200, Port 2 acted as an RS485 gateway (9600, 3825 ms delay) to other daisy-chained meters, with address 1 reserved for the meter itself. The 1450 has no such thing: every device that hung off that gateway now needs its own IP or an external RS485/Ethernet converter.

Two warnings from the manual that save a site visit: Modbus RTU does not work through a modem (that port must be set to Modbus ASCII at 9600 with no flow control), and any port feeding a P40N+/P41N+/P43N+/P70N display must be at 9600, address 1.

4. I/O modules: addressing, power and wiring

The external modules are the same on both platforms (manual E134-7-15), so the practical rule is to reproduce on the 1450 exactly the I/O Modules table of the 1250: same row number, same identifier, same address and same port. If the physical modules are new, they have to be re-addressed to match.

Factory addresses and the bus rule. Each module type ships with a fixed address: 128 (1mAON4/8), 132 (20mAON4/8), 136–148 (8AI1–4), 156 (4RO1), 160 (4PO1) and 164 (8DI1), all at 57600 baud. Two modules of the same type on the same port answer simultaneously, and the address of one of them has to be changed. Port 3 and Port 4 are independent Modbus buses, so the same address can be repeated across ports without conflict.

Power budget. The meter delivers a total of 12 VA for modules through its RS485 ports, with a maximum of four modules and only two analogue ones (E134-7-15 §2.2.3, E171701 §10.6.1). Rated consumption: 20mAON4 5.0 VA, 20mAON8 8.5 VA, 4PO1 2.7 VA, 1mAON4 2.7 VA. With four analogue modules an external PSIO supply is needed (90–240 V AC/DC, 12 V DC output, 12 VA, up to four modules); for 24 or 48 V DC auxiliaries, EIG specifies the PB1 instead of the PSIO. The modules’ side ports pass RS485 and power along the whole group, and the manual does not contemplate mixing meter and PSIO within one physical group, so each supply feeds its own group.

Split for the typical case, with a single PSIO:

The meter powers the 4PO1 and the two analogue modules with the fewest loops (2.7 + 5.0 + 5.0 = 12.7 VA by the tables, but 5.0 VA is the maximum with all four loops active; with five loops out of eight the actual load stays below 12 VA). The PSIO powers the two most heavily loaded analogue modules (10 VA). If the meter were to reset the I/O bus for lack of power, plan B is to swap the 4PO1 with one of the analogue modules on the PSIO, or to add a second PSIO.

How to change a module’s address (E134-7-15 §2.2.2, §2.2.3.1, ch. 4). Always with the module on its own, before coupling it to the group:

1. Power the module via +V/−V (PSIO or a jumper lead from the meter) and connect A(+), B(−) and S to an RS485-to-USB converter on the PC.
2. In Communicator, Connect with the current address (132 on a new 20mAON4), 57600, 8-N-1, Modbus RTU.
3. I/O Devices › Stand Alone Programmer: change Address (133 or 134 in the typical case). Leave 57600 and 0 delay so that they match the meter port.
4. Send: the module restarts with the new address. Label it with identifier and address before mounting it.

If the address is unknown, hold Reset for 3 s: the module answers at address 247 at 57600 for 30 s. With any Modbus master (FC06/FC16) it is also possible to write register 45057 (address), 45058 (baud rate: 0=4800, 1=9600, 2=19200, 4=57600, 5=115200) and then any value to 65410 to restart.

Wiring. Meter RS485 port terminals, left to right: +V · −V · S · − · +. Terminals on the female side port of the first module: A(+) · B(−) · S · −V · +V. The correspondence is + → A(+), − → B(−), S → S, +V → +V, −V → −V. The group powered by the meter receives all five wires; the PSIO group receives from the same bus a branch of only A(+), B(−) and S, and the PSIO always goes on the right of its group, plugged into the male port of the last module. S is shield, not earth: it is earthed at a single point per bus. 20 AWG shielded cable; RS485 up to 1,220 m, but above 60 m EIG calls for a remote supply and 120 Ω termination at both ends. Mounting with one MBIO kit per group: left-hand module to the bracket with a PEM nut, slot the following ones in, tighten and close with the right-hand bracket; panel or DIN rail with the clips.

5. Transferring the profile and the analogue scaling

The 1250 profile cannot be loaded as is into the 1450: they are .nps files from different platforms. What you do is open the 1450 profile in Communicator and reproduce, block by block, what the 1250’s Device Profile Report says. In order:

1. General Settings › CT, PT and System Hookup. CT and PT ratios, hookup (3 element wye, 2.5 element or delta), nominal frequency. These are the values that set every scale that follows.
2. Communications. Port 1 for the PC; Port 3 and Port 4 at 57600, Modbus RTU, 8-N-1, 0 delay, Master (I/O Modules) mode; Port 5 with the plant IP the meter is going to have (the factory one is only good for the bench).
3. I/O Modules. The five-row table from the previous section, with the same number, identifier, address and port as on the 1250.
4. Limits, Log Settings and Full Scales. Copy limits, historical log intervals and waveform full scales; the 1450 adds logs and options that did not exist before, which are left at their default values.
5. Channel assignment of each module, by hand, from the screenshots taken on the 1250.

Analogue scales are entered in secondary quantities. The External Module Programmer dialogue warns you: for voltage, current and power, the values at 4 and 20 mA are given in meter secondary quantities, not plant values. The conversion comes from the ratios in the profile. In the typical case, with CT 1,200:5 and PT 15,000:110, k_i = 1,200 / 5 = 240, k_v = 15,000 / 110 = 136.36 and k_p = k_i · k_v = 32,727.3.

A full scale of ±30 MW is programmed as ±916.6667 W secondary (30·10⁶ / 32,727.3), and ±20 MVAr as ±611.1111 var. It is worth calculating the exact value once and using it identically on every module that outputs the same quantity: two modules with 916.6667 and 916.6700 are saying the same thing, but on a later review they look like an error.

Assignment for the typical case (0.05 s quantities, i.e. instantaneous readings):

Unassigned channels are left as Not Assigned; the dialogue fills them with 20.0000 / 4.0000, which is not a real scale and does not need correcting. Before replicating each channel it is worth checking it against the meter’s full scale: a phase-voltage channel set to 45 → 55 would be saturated in normal service (nominal 63.5 V secondary) and is almost certainly a frequency band assigned to the wrong quantity on the old unit. The migration is the moment to correct it, not to copy it.

KYZ outputs (4PO1). Each output is assigned to an energy accumulator and a pulse weight. Typical case: output 1 kWh delivered, output 2 kWh received, output 3 kvarh delivered, output 4 kvarh received, at 10 kWh or kvarh per pulse. The weight is chosen so that at full load the pulse rate stays within what the receiving counter accepts; at 30 MW and 10 kWh/pulse that gives 3,000 pulses per hour, less than one per second.

What changes from the 1250 on saving. The 1450 profile carries the reset list with Reset Unit to Boot Mode — Default Communications Settings enabled: it is best left that way, because it allows a badly programmed port to be recovered from the reset button. Saving the 1450’s .nps and its Device Profile Report alongside those of the 1250 closes the migration documentation.

6. Commissioning and verification

The sequence that gives the fewest surprises is to do everything on the bench with the 1450 on auxiliary supply and the modules mounted, and to bring an already tested assembly to the panel. Since the 1450 occupies the same cut-out and repeats the 1250’s terminal layout, the change in the panel is a disconnect and reconnect: voltages, currents, L(+)/N(−) auxiliary and the serial port leads are moved wire by wire to the same terminals, with the same crimps. Before disconnecting, photograph the 1250’s terminal strip and short the CT secondaries at the test block. The recommended external fuse is still 5 A / 250 V slow-blow, with an independent earth (never through the negative of a DC supply).

1. Check the control power suffix on the 1450 label (D2 for 96–276 V AC/DC, D for 18–60 V DC) against the panel auxiliary supply.
2. Re-address, one at a time and on their own, the modules that need it (133 and 134 in the typical case) and label all five with identifier and address.
3. Assemble the physical groups between their MBIO brackets: 4A (KYZ Module 1 + AO Module 3), 4B (AO Module 1 + AO Module 2 + PSIO on the right) and Port 3 (AO Module 4).
4. Wire the leads and the 4B branch; shield earthed at a single point per bus.
5. Power the PSIO and the meter. Check that 4A and Port 3 start with the meter alone and 4B with the PSIO alone: a group that starts from the wrong supply has +V/−V where it should not.
6. Connect over Ethernet (FIXED, 10.0.0.1) and load the prepared profile: CT/PT, communications with Port 3 and Port 4 as Master (I/O) at 57600, I/O Modules table, limits and logs.
7. Open each module from Device Profile › I/O Modules › Edit and enter the channel assignment and the secondary scales; Send on each one.
8. Verify: TX/RX LEDs flashing on all five modules; with the meter unloaded, each voltage and current loop should read 4.00 mA and the power loops 12.00 mA (zero at the centre of the bipolar scale). Measure with a load of ≤ 500 Ω per loop.
9. With a secondary injection set, apply 110 V and 5 A and check 20.00 mA on the line-voltage and current loops, and that the WebView reading matches the injection in primary terms (15,000 V, 1,200 A).
10. Leave the assembly running for half an hour and check that the meter does not reset the I/O bus (the modules do not all flash at once or disappear from the table). If it does, apply plan B of the power split.
11. Program the plant IP, return the switch to PROG, save the final .nps and the Device Profile Report, and seal.

All that remains in the panel is the physical swap of the meter, the connection of voltages, currents and auxiliary supply, and the connection of the 4–20 mA and KYZ loops to the control system following the inventory from the start.

7. Common problems

Sources

• Electro Industries/GaugeTech, Nexus 1250/1252 User Manual, Doc# E107706 (§5, §9.4, §11.2).
• EIG, Nexus 1450 User Manual, Doc# E171701 (§1.5, §3.5, ch. 4, 5, 9 and 10).
• EIG, Nexus 1450 Quickstart Guide, Doc# E171703.
• EIG, Modbus Communicating I/O Modules Manual, Doc# E134-7-15 (ch. 2 and 4).
• EIG, Communicator EXT / CommunicatorPQA User Manual, §2.2.
• Original documentation at electroind.com.