When do I use a Terminating Resistor while communicating over an RS485 Bus?

Termination is used to match impedance of a node to the impedance of the transmission line being used. When impedance is mismatched, the transmitted signal is not completely absorbed by the load and a portion is reflected back into the transmission line. If the source, transmission line and load impedance are equal these reflections are eliminated. There are disadvantages of termination as well. Termination increases load on the drivers, increases installation complexity, changes biasing requirements and makes system modification more difficult.
The decision whether or not to use termination should be based on the cable length and data rate used by the system. A good rule of thumb is if the propagation delay of the data line is much less than one bit width, termination is not needed. This rule makes the assumption that reflections will damp out in several trips up and down the data line. Since the receiving UART will sample the data in the middle of the bit, it is important that the signal level be solid at that point. For example, in a system with 2000 feet of data line the propagation delay can be calculated by multiplying the cable length by the propagation velocity of the cable. This value, typically 66 to 75% of the speed of light (c), is specified by the cable manufacturer.
For our example, a round trip covers 4000 feet of cable. Using a propagation velocity of 0.66 × c, one round trip is completed in approximately 6.2 µs. If we assume the reflections will damp out in three “round trips” up and down the cable length, the signal will stabilize 18.6 µs after the leading edge of a bit. At 9600 baud one bit is 104 µs wide. Since the reflections are damped out much before the center of the bit, termination is not required.
There are several methods of terminating data lines. The method recommended by Electro Industries is parallel termination. A resistor is added in parallel with the receiver’s “A” and “B” lines in order to match the data line characteristic impedance specified by the cable manufacturer (120 ohms. is a common value). This value describes the intrinsic impedance of the transmission line and is not a function of the line length. A terminating resistor of less than 90 ohms should not be used. Termination resistors should be placed only at the extreme ends of the data line, and no more than two terminations should be placed in any system that does not use repeaters. This type of termination clearly adds heavy DC loading to a system and may overload port powered RS232 to RS485 converters. Another type of termination, AC coupled termination, adds a small capacitor in series with the termination resistor to eliminate the DC loading effect. Although this method eliminates DC loading, capacitor selection is highly dependent on the system properties. System designers interested in AC termination are encouraged to read National Semiconductors Application Note 903 located at http://www.national.com/an/AN/AN-903.pdf for further information.

I am using another Manufacturer's RS232 to RS485 converter and I cannot get it to communicate with the Nexus® meter. What is the problem?
.

Before we answer this question, let me explain about the two types of converters that are typically used. The first is your basic interface only converter, and the second is a converter that supports Send Data Control. What determines the type of converter that is used is the software that is being used with the converter and the cost.

Basic Converters
The basic interface only converter needs RTS Control. RTS Control is relevant only if you are converting to 2-wire RS485 (where the converter is a Master or a Slave) or to 4-wire RS485 (where the converter is a Slave). RTS Control is a method with which the RS232 device (typically a PC) tells an RS232-RS485 converter when it should enable its RS485 driver, i.e. when it should be transmitting. On a converter, which is an interface converter only and does not monitor the data, an external signal is required. When providing RTS Control, the RS232 device raises its RTS output immediately before it starts to communicate, and drops it after the last stop bit of the message has been transmitted. The converter uses this signal to control its RS485 driver. The advantages of using RTS Control is that the converter is simpler and therefore cheaper, and it does not care about the baud rate (within its limits) or the number of bits, parity, etc. If this was the case with software, or with an RTU, there would be more set up decisions on the software in order to communicate with a meter increasing the software’s difficulty and decreasing speed due to longer delay times. This is not the best solution and often is the cause of the problems in the field. It is better to have a converter that automatically controls the RTS signal, thus eliminating software and RTU additional requirements.

The following diagram illustrates a message comprising of two characters and the RTS Control signal, which would be required to successfully transmit this message. Both characters are shown as 8-bit data (or 7 bits with parity).

When using Communicator EXT or any other Electro Industries software the converter that supports automatic Send Data Control should be used.

Converters with Automatic RTS Control
A more sophisticated converter, e.g. the Electro Industries Unicom 2500, does not need RTS Control from the RS232 portion because it generates the control signal internally by monitoring the data with a microprocessor. The Baud rate, and the DCE and DTE switch is all that is required to set on the Unicom 2500 converter. The converter does the rest. This is considered the superior because it is significantly easier to configure and is not dependent on the configuration of the software and the RTU. Electro Industries recommends this solution exclusively, not just to our devices, but for ALL RS485 speaking devices. Better converters provide better capability, easier use and more reliability.

The Electro Industries Unicom 2500 is an industrial converter that uses automatic Send Data Control. it is also available with an optional Fiber option. This converter, additionally, is optically isolated to 2500 volts to protect the remote devices from destructive electrical anomalies. For more information, the brochure is located at: http://www.electroind.com/pdf/Unicom2500_118702.pdf or for the manual http://www.electroind.com/pdf/unicomman.pdf.

What is the sample rate of the High Speed (HS) inputs?

The Nexus® 1250 meter will sample the HS inputs at up to 2 independent rates, depending upon the configuration of the unit. The HS inputs can be used for either pulse accumulation or for status change to record a waveform. The HS inputs are always sampled at 100 times per second, and debounced for 2 sample times. Your pulse rate needs to be within its tolerance. If the Nexus® meter has been ordered with the optional 2 meg or 4 meg memory and the user has selected the HS input to be used for waveform recording, the HS inputs are sampled at a rate that is based upon the user selected waveform sample rate which is much faster than the pulse counting rate. The unit will record the waveform instantaneously based on the change of a status input.

How can I communicate with the Nexus® 1250 Meter?

The Nexus® 1250 meter has four communication ports, three are designed to use the RS485 interface, and one is bidirectional between RS485, and RS232. For direct connections, it is easy to use the RS232 port, and a standard serial extension cable (straight), or using an RS485 to RS232 converter, such as our Unicom 2500, connect to any of the RS485 ports. The Nexus® 1250 Meter can be remotely located, and using an external or the optional internal modem, be accessed across the PSTN with standard dial-up modems. The meter can also talk across a LAN or the Internet using the internal TCP/IP network interface. Additional interfaces include Modbus RTU, Modbus ASCII and DNP 3.0.

What is the response time (RTU function) from condition change to status output change?

Response time is typically less than 200 mSec. per Output Module, and can be extended to many seconds by programming additional delay times, associated with individual outputs. Many factors may also influence this response time. The number of Output Modules connected to the Nexus® meter (each will be polled in turn, and time between polls depends on the module type and the amount of information that must be retrieved or set), the baud rate of the communications between the Nexus® meter and the Output Module.

What is the VAUX input used for?

This is an independent voltage input that has all the capabilities of the other voltage inputs (recording, triggering, trending, etc.). A typical use would be in synchronizing a line closure. With the Nexus® meter connected to one side of a breaker, the VAUX can be connected to the other side of the breaker, and using the real time phasor display of the meter, watch the VAUX phasor relationship to the other inputs. Another application would be to use the Aux voltage to provide you the potential from neutral to ground. This enables a user to test the grounding system of a substation or facility.

Can I change the relay modules connected to the Nexus® meter and manually change the state of them through the Modbus registers?

How does the DNP Level 2 dead band percentage work in my Nexus® 1252/62/72 meter?

Understanding Deadband %

In the Communicator EXT software, the users can customize the DNP object map. From Analog Input data (Object 30), Analog Event data (Object 32) can be created by its Deadband percentage. Deadband percentage values set the limit for event data. This Deadband percentage value can be calculated from the Full Scale value. The following example will explain the usage of Deadband percentage.

Example: The Nexus® 1252 meter has the following setup in the programmable settings.

<Figure 1. Full Scale Values>

Example for Current
From the figure 3, the Deadband percentage is 1.00 % for all readings. The range of Deadband percentages are from 0.01 % to 326.67 %. For the IA, IB, IC, the full scale is 800.00. The 1 % of 800.00 is 8.00. Analog input data is scanned after 5 second of meter power up. After that, new Analog input data is scanned every second or faster (For tenth second readings). If the value changes by this Deadband percentage, the event data will be created. For example, IA is 200.00 A after 5 seconds of meter power up. After that, newly scanned IA reading will be compared with 200.00 A. If a new IA reading becomes 208.00(1%) or higher, the event data will be created. After that, the new IA readings will be compared with 208.00 A. This is the same for the opposite direction. If the reading becomes 192.00A or lower, the event data will be created. After that, new IA readings will be compared with 192.00 A.

Internally, the meter measures the readings in secondary. From the figure 2, the IA has the ratio of 800.00:5.00. This means that the Nexus meter reads 1.25A secondary for 200.00 A Primary. It is 0.05 A change for 1 % Deadband internally. All computations are scaled down by CT and PT ratios.

Example for Voltage
This reasoning is the same for the Voltage readings. For the VAN, VBN, VCN, the full scale is 6351.00. The 1 % Deadband is a change of 63.51. If the voltage reading changes by 63.51 V, the event data will be created. The ratio for voltage is 7200.00:72.00. That means that 1% Deadband is a change of 0.6351 V internally.

Example for Power per phase
Power Phase has 9600.00 k full scale. 1% Deadband is a change of 96.00k. Therefore, if the power readings (Watt, VAR, VA) change by 96.00 k, the event data will be created. The power phase ratio is 16,000:1 from CT, PT ratios (160:1, 100:1). Internally, 1% Deadband is 6. 1 % Deadband is tight for power readings. The event data will be created by small changes of phase angles between voltages and currents also.

Example for Power total
The Power total has 28.80 M for full scale. 1 % Deadband is 0.288 M. Therefore, the event data will be created if Power total changes by 288 k (Watt, VAR, VA). The ratio for Power Total is also 16,000:1. Internally 1 % Deadband is 18.

<Figure 2. CT and PT ratio>

< Figure 3. DNP Customized Map>

How do I get the GE SC-6 (USB to Optical Converter) to communicate to my Nexus™ Socket Meters?

I am setting up the MV-90 TIM for the Nexus® meter and I need to know the weight of the pulse?

MV90 requires that the pulse weight be set to one 1, but remember along with the pulse weight you need a correct multiplier for a correct read.

Here is an example:

CT 200:5 or 40:1
PT 7200:120 or 60:1

40 x 60 =2400

2400 x unit pulse weight (1) = 2400

MV-90 requires the multiplier to be divided by 1000 before entering it MV-90 therefore

2400 / 1 = 2.4 multiplier that also must be entered in MV-90

So in conclusion the pulse weight is 1 and if the multiplier is not entered properly the value measured will not be right. In the example above the multiplier is 2.4.

What is the CPU-1000?

The CPU-1000 is the component of the Futura+ that you connect the monitored voltages and currents to. It is the 'black box' where all the analog to digital conversion and digital signal processing, and data logging takes place. It houses any optional memory and event inputs and relay output circuitry. In addition to the CPU-1000, a typical installation adds one or more display modules.

What display options are available for the CPU-1000?

There are many available displays for the Futura+. They range from a single row of LEDs to three rows with multiple additional enunciators.
P-11 - This is a single function display, available for any measured value.

P14 - This display shows real power (Watts), Total kilowatt hour (WH) and watt demand (WD).

P15 - This display shows VAR / VARH / VARD with 6 digits of resolution.

P31 - Amps module displaying phases A-B-C and N. Also displays %THD for each reading.

P32 - Volts module displaying A-N, B-N, C-N phases, THD and K-Factor. Can also display phase-to-phase readings.

P33 - Power module displays KW, KVAR, VA and PF. The lower sector can be turned off for a dual Watt / VAR display.

P34 - Multifunctional digital display with a simultaneous 3-phase presentation of voltage, current and power. It also displays %THD and K-Factor for each voltage and current reading.

How many displays can I connect to the Futura+?

The Futura+ can directly power up to four display modules from the internal power supply of the unit. Many more displays can be driven if an external power supply, such as our Power Brick PB1-9VO available with voltage input range of 12 to 60 VAC/DC (D) or 90 to 240 VAC/DC (D2), is used to supply power to the displays.

If the display or cable to the display is running outdoors for more than two hundred feet an opto-isolator such as EIG’s ISO–485 is recommended. This isolates the meter base from the displays and avoid grounding loops for long display runs. Note the Nexus® 1250 meters have this function built-in. Thus, this is only required for a Futura+.

View the .PDF file to get a wiring diagram

How do I communicate with my PDA1000, CPU1000 or DM Series Meter Using Futura+ Communicator?

It is a common complaint that people, when using Futura+ Communicator, do not know how to connect to the unit with the software. The most common scenario is:

This usually means that the setting for signing on or the meter setting are not configured properly.

Below is the information needed to communicate with any of the devices.

1. Baud Rate (Ships from factory as 9600)
   
   
2. Address (Ships from factory as 0001)
   
   
3. Protocol (Ships from factory as EI)
   
   
4. Cable (Straight through NOT a cross over cable/null mode
   
   
5. Computers Com Port (all computers are different typically 1 sometimes 2 or 3)

Typical Reasons Communication Cannot be Established

1. User changes factory defaults (Address, Baud Rate, Protocol) and forgets what they changed them too.
   
   
2. Cable is bad or user is using a cross over cable (null modem)
   
   
3. User has computer on wrong Com Port. To check your COM ports, go to Control Panel/System/Device Manager/Ports (com & LPT)
   

1. Check the Futura+ Communicator Setting
   
   
2. Check the Meters setting through the faceplate
   
   
3. Check your serial cable. People using a null modem cable is the single biggest customer support issue.

Note: It is highly unlikely that the meter is defective. Often, after trying these suggestions, EI customer support can usually get it working with you over the telephone.

Modem Communication Note:

If you are using these metering devices with an external modem, there are many additional configuration issues that need to be addressed. Since this is a daunting task, EIG designs a Modem Manager product that is an RS485 to RS232 converter with built in functionality so that you do not need to program the modem. You can purchase this product at the factory. We can rush one out to you ASAP to solve any modem programming issues. It has been our experience that the Modem Manager will solve almost 100% of the modem communication problems in the field. This will also work with ANY RS485 device and will solve the problems in the field. This has been a savior for many of our customers (even with competitor’s products).

Nexus® meter users don’t experience these problems with the Nexus® meter's internal modem because we built Modem manager right into the Nexus® meter.

How do I program the DMMS350 with my desired IP address?

1. Connect the DMMS350 Ethernet port directly to a computer with a crossover
   cable or through a hub with a straight Ethernet cable.
2. When running more recent versions of Windows you should be verified that a
   network connection has been established. The link light (LK) on the DMMS350
   should also light up when the connection has been established.
3. Open the dos command window from Start Menu -> Run… -> cmd
   
   
   
4. Type “arp –a” if table contains an IP address skip step 5.
5. If empty arp table type “arp –s 0.0.0.0 00-00-00-00-00-00” to create a generic arp
   entry. Type “arp –a” again and verify you now have a internet address.
   
   
   
6. Assign your desired IP address by typing “arp –s (desired IP address) (mac
   address). In example below IP address is 135.15.173.39, mac address 00-20-4a-
   74-52-15. DO NOT FORGET THE SPACE BETWEEN IP AND MAC
   ADDRESS
   
   
   
7. Type “telnet 135.15.173.39 1” It should fail in under 5 seconds. (substitute your
   IP address)
8. Type “telnet 135.15.173.39 9999”
9. You have now programmed your DMMS350 Ethernet card. You can exit the
   telnet screen.

How do I get my DMMS+ to read a lower current or voltage?

Refer to the meters instruction manual to get in the programming mode. Once in the programming mode follow the steps outlined below.
Go to E by pressing the max/min/ limits button
Press volts until a 5 is displayed

Press Amps once, you should see E0 on top and a value such as 0255 on the bottom.

Press min/max/limits until you see E7 on the top than press Amps.

A value should be displayed in the center. This value will vary depending on when you purchased the meter. One of three different values will appear (0044, 0075 or 0099). The first number indicates the threshold for voltage and the second number is for the current. Let's use 0075 as an example. The 7 is a number when doubled equals 14 this would be the approximate lowest threshold voltage the meter can read. The 5 is a number when doubled equals 10 which represents the approximate lowest current the meter can read. To change the threshold for current you will only need to adjust the 5 and not the 7. If are adjusting the voltage you need only to adjust the 7 and not the 5.

To adjust one of the two numbers press volts until the desired number appears at the bottom of the display then press amps to save that digit. Press volts again to select the desired second digit than press amps again. The new value should be displayed at the bottom of the screen now. I would suggest lowering it in steps, one digit at a time. CAUTION: Do not bring these numbers down to zero or too low the meter will pick up too much noise.
To exit press min/max/limits until EE is displayed on top press amps twice and try it. If further support is needed contact customer support at 516-334-0870 or e-mail at support@electroind.com.

How do I trouble shoot wiring errors with the DMMS 300+?

The DMMS 300+ is capable of troubleshooting wiring mistakes. If the meter is in Delta mode you will need to program it, temporarily, to WYE. If you have negative power readings, low power factor, large amount of neutral current, you can use certain functions of the DMMS 300+ to determine the cause of the problem.

Trouble Shooting Negative Power Readings:

While in WYE mode press the "Power" key and most of the light under the "Power" label should light up. Press the "Phase/Next" until the LED for "kW" or "MW" lights up. Now press the "Power" keys and do not release it. You should be able to observe at that instant the total power for each phase. You should see the individual lights under the "AMPS" label light up and a value of "kW" or "MW" displayed on the bottom display. If one of the is negative, that would indicate that you have a reversed wire on one of your "CT's". However before you change the wiring on your CT please review the following instructions.

Phase Reversal Detection

If your phase current A and your phase voltage A are not on terminal 8,9 for current and terminal 5 for voltage, the meter might be flashing an alarm to indicate that it is so. Pressing the " Max/Min/Limits" key until the Limit light that is flashing is lit and immediately after press the "Phase/Next" key will indicate whether or not you have some kind of phase reversal. In addition, you can do the same test on power factor and see if you have at least 0.7 power Factor or above on all the phases. If you notice a reading of for example: A= 0.9 B=0.5 C=0.2 you should try reversing B and C phase voltage. You should see a positive change in your power factor readings. You then check your individual power for each Phase and swap the current wires if you see a negative power reading. The Rule here is to check voltage wiring first then current.

What are some programming tips for the DMMS 300+ equipped with Analog output modules?

Upon receiving your meter already mounted with an Analog Output module, you might want to change the programming if the factory default is not to your liking or reset it to factory settings. For wiring diagrams and others programming questions please go to this URL address http://www.electroind.com/pdf/DCAnalog.pdf . You will also need the DMMS 300+ installation and operations manual to enter the programming mode. Use this URL address to retrieve the manual http://www.electroind.com/pdf/DMMS300350Manualrev4.8.pdf.

Follow the instructions provided by the installation and operations manual to get into the programming mode. The page to go to is page 41 of the installation and operations manual. Upon entering the programming mode you should see the number "0." Press the Max/Min/Limit key until you get to "8." Press the "Amps" key you should then see "8P.0" appear at the top of the DMMS 300+ display and four vertical bars on the bottom of the display.

Factory Defaulted Analog Output Modules

The 6 and 10 Channel Analog output modules store their calibration information on a memory chip that is located on the analog output module itself. These Analog output modules are SEFI-1, SEFI-20, SHNI-1, and SHNI-20. To retrieve the calibration information from these outputs to your meter press the "Amps" key while at "8P.0" and you should see the vertical bars at the bottom of the display move up to the mid-section of the display. Once you reposition the bars on the bottom of the display to look the same as the middle of the display, press the "Amps " key, the information on the module is now transferred into the meter. Note: the 2 and 4 channel modules do not have factory storage capability.

A Simple Way To Get Your 6 Or 10 Channel Module Up And Running When You Programmed It Wrong

For example, if you have a unit that is in saturation or showing a large amount of current (i.e. 2 milliamps (for a 0-1mA) or 23 milli amps (for a 4-20mA), and you have another unit with a module that is working.) You can retrieve the default calibration information from a working module using the above step. Without exiting the program, remove the good analog output without disconnecting the control voltage to the meter, and attach the output that is saturating. Exit out of the program while the saturating unit is attached to the DMMS 300+. This automatically stores the good data from meter to the saturating module. Therefore the calibration data will now be back in the saturated module and will start working properly as long as the voltage range of the two meters are the same, if not see below.

The Importance 8P.0 In The Programming Mode

The position of the vertical bars on the bottom of the display lets the DMMS 300+ meter know the type of output that is attached to it and also indicates to the analog output the voltage range of meter that is present. Example: 150volts L-N, 300volts L-N, 75 volts L-N. The analog output will output differently depending on the DMMS300+ voltage range. For example 0 to 150 volts L-N = 0 to 20mA or 0 to 1mA. This is important to note because if the saturated module was calibrated for a different voltage range unit, the above procedure will not work. You will need to adjust the first two vertical bars from left to right for the appropriate voltage range.

Is there a quick reference guide to get into DMVA 100 to change the PT and CT ratios?

The DMVA 100 is password protected. To enter the programming mode, key in the following password. The password is 555.

NOTE: THE METER WILL NOT STORE ANY PROGRAMMING UNLESS PROPERLY EXITED.

ENTERING THE PROGRAMMING MODE:

Step 1:

a. Press PRINT/PROG until 3 appears in lower display.
b. Press PHASE/NEXT to select.
c. 333 appear in lower display.

Step 2:
a. Digits begin scrolling in upper display. The password is 555.
b. Press PHASE/NEXT each time 5 appears.
c. The selected digits appear in lower display.
d. Display blanks and PPP flashes in upper display, confirming a correctly entered password.
e. PPP is replaced by 0. The meter is now in the Programming Mode, GROUP 0.

GROUPS, Functions, and Switch PACKS:

• GROUPS are the main category.
• Functions are sub categories of GROUPS.
• Switch PACKS are sub categories of Functions.

BUTTON	FUNCTION	DESCRIPTION
MAX/MIN/LIMITS	ADVANCE	Scrolls groups, functions, and advances to exit point from function and group level.
PRINT/PROG	CHANGE VALUE	Scrolls packs, digit counters, and changes Switch PACK position UP or DOWN.
VOLTS	STORE	Activates new data entry, stores digits, and enters or exits from group or function level.

To change the VOLT OR AMP FULL SCALE settings (Function 0 and 1, respectively), follow these steps:
NOTE: PRESS MAX/MIN/LIMITS, AT ANY TIME, TO CANCEL BEFORE STORING THE LAST DIGIT OR SWITCH.

Step 1:
a. Enter Group Level of Programming Mode,
b. Press MAX/MIN/LIMITS until 1. appears in upper display.
c. Press VOLTS to activate the Group.

Step 2:
a. 10. appears in upper