How to Replace Discontinued RTUs Without Rewiring a Site

By Andrew Erickson, Application Engineer at DPS Telecom

You can replace a discontinued remote terminal unit (RTU) without re-terminating any alarm points if the new unit matches the existing one in two places. It has to take your existing cables, with every pin carrying the same alarm point it carried before. It also has to report to your alarm master in the protocol the master already uses. When the new unit matches on both, your field wiring stays punched down where it is. The technician at each site only moves cables from the existing unit to the new one.

At DPS Telecom, our engineers build replacements for discontinued RTUs, including units from other manufacturers. We study the existing unit's pinouts, protocols, form factor and inputs, then build or configure a unit that plugs into the wiring already at your sites. Our goal on those projects is zero re-wiring at the remote site.

Can a New RTU Connect to Your Existing Wiring Without Re-Terminating?

A new RTU can connect to your existing wiring without re-terminating anything when it accepts the same amphenol cables and each pin carries the same alarm point it did on the discontinued unit. The cables from your 66 blocks plug into the new unit, and nothing on the blocks changes.

A matching connector doesn't guarantee a matching pinout. Say the pair carrying a generator alarm landed on discrete input 5 of the discontinued unit and lands on input 12 of the new one. The cable plugs in without any trouble, but your alarm master now shows the generator alarm under input 12's description, which belongs to some other piece of equipment.

Some RTUs use two pins for each alarm point, one for the alarm and one for its return. Others use one pin for each alarm point and tie all of them to a single common return pin. Our own NetGuardian RTU line has both. The NetGuardian 832A uses two pins per point, and the NetGuardian 864A uses one pin per point with a common return. An 832A's cable moved onto an 864A doesn't put the alarms on the right inputs, even though both units use 50-pin amphenol connectors. A replacement has to be matched pin by pin.

What to Document About the Existing RTU Before You Choose a Replacement

Write down everything the existing unit connects to before you talk to a replacement vendor, because each item on the list is something the new unit has to match. If your sites aren't all wired the same way, document each variation separately.

• Make and model. Record the make, model and hardware revision. Photograph the front and back panels as well, because the photos show every connector on the unit.
• Connector types and pinouts. List every connector and what it carries, and record which pin carries which alarm point. The user manual usually has pinout tables. Where it doesn't, a technician can trace pairs from the punch block.
• Discrete input wiring style. Note whether each alarm point uses two pins, one for the alarm and one for its own return, or one pin with every point sharing a common return.
• Normally open or normally closed. For each discrete input, note whether the contact is normally open or normally closed. On a NetGuardian, discrete inputs default to normally open, and you can set any point to normally closed in the unit's alarm point configuration. That setting goes in with the rest of the configuration at the shop, so no wiring changes at the site.
• Dry contact or voltage. For each discrete input, also note whether it's a dry contact or whether the alarm source puts voltage on the line. The new unit has to read the same kind of signal.
• Analog inputs, control relays and serial ports. Count each kind and note how many are in use. For analog inputs, note what each one measures and its range. For serial ports, note what's attached.
• Protocol and transport. Record the protocol the unit uses to report to your alarm master and how those reports travel, whether over a network, a serial link or a dial-up line.
• Power input. Note the voltage, the polarity and whether the unit is fed from one power source or two. Many telecom sites run on -48 volts direct current (VDC), but not every site does.
• Mounting and rack space. Measure the rack width and the vertical space the unit takes up, and note which side the cables come in from.

Documenting a site can also show that rewiring is the better choice. If the field wiring is damaged, or nobody can say which pair goes to which piece of equipment, plugging a new RTU into it carries the same problems forward. At a site like that, re-terminating while you're there gives you wiring you can trust and documentation that matches it.

What If the New RTU's Connector or Pinout Doesn't Match?

If the new RTU's connector or pinout doesn't match, you can still leave the field wiring alone in one of two ways. Adapter cabling connects a standard RTU to your existing amphenol cables, wired so each alarm point reaches the right input. A custom-built RTU has the discontinued unit's connectors and puts each alarm point on the same pin it used before.

We often build project-specific adapter cabling as part of a replacement. When the protocol or form factor you need isn't already in our product line, our RTU replacement service engineers it. Before we manufacture a custom unit, we send you a virtual prototype, a photo-realistic image of the finished unit, so you can check the connector positions against your racks and cables.

"The thing I liked was that DPS was going to make it fit our needs. They were going to make their stuff fit ours."

Lead Telecom Tech, Electric Utility

Will the New RTU Work With Your Alarm Master?

A new RTU will work with your existing alarm master if it reports in the protocol your master already uses, or if you add a master that can read both protocols. Our NetGuardian RTUs report in Simple Network Management Protocol (SNMP), Transaction Language 1 (TL1), Distributed Network Protocol 3 (DNP3) and Modbus, along with a broad range of older protocols. If the discontinued RTU came from another manufacturer, we can replace it as long as we can match the protocol your alarm master uses to collect alarms.

When your current master can't read the protocol the new RTU uses, an alarm master that reads both can collect the alarms instead. Our T/Mon alarm master reads many standard and proprietary protocols and serves as the central point that collects alarm data from across your network. New RTUs and the discontinued units you haven't replaced yet can then report to the same place while you work through your sites.

If your alarm master is discontinued too, you're replacing more than RTUs. We cover that larger project in our guide to replacing discontinued monitoring equipment.

How to Cut Over to a New RTU Site by Site

Testing each site's kit on a bench first means problems turn up at the shop instead of at the site. Each site then goes without monitoring only while the technician moves the cables, and the technician is at the site for that whole time.

1. Build the point map. For every alarm point, list the punch block position, the pin and point number on the discontinued unit, the pin and point number on the new unit, whether the contact is normally open or normally closed, and the description and severity at your alarm master. Every later check is made against this map.
2. Preconfigure the new unit. Load point descriptions, normally open or normally closed settings, alarm thresholds, network settings and reporting destinations at the shop, before anyone travels.
3. Add a second reporting destination if alarms will go to a new manager. If the replacement also sends alarms to a new SNMP manager or a new alarm master, configure the new RTU to report to the existing destination and the new one at the same time. The NetGuardian 832A G4, for example, can send alarms to T/Mon and to several SNMP managers at once.
4. Bench-test one full kit. Set up one complete site's kit on a bench, with the RTU, its cables, any adapter cabling and a test punch block. One person triggers every input and operates every control relay while a second person at the alarm master confirms that each alarm arrives with the right description and clears when it should. A problem found on the bench gets fixed at the shop, without a trip to a site.
5. Pilot at an easy-to-reach site. Do the first swap at a site you can drive to. Field wiring doesn't always match its documentation. If a pair turns out to be on a different punch block position than the point map says, a technician only has a short drive back to correct it.
6. Tell the alarm master's operators, then swap at the connector. Let the people watching the alarm master know the site will be offline for the swap. Unplug the amphenol cables and power from the existing unit, mount the new unit and plug the same cables into it.
7. Check every point before leaving. With the person at the alarm master on the phone, the technician triggers each input on the point map. Each one has to appear at the master with the right description and severity, then clear. If a point fails and can't be fixed at the site, plug the cables back into the discontinued unit, which brings monitoring back the way it was, and take the problem back to the bench.
8. Remove the existing destination. If you set up a second destination in step 3, compare the alarms arriving at both. Once they match, delete the existing destination from the new RTU's configuration and remove that site's entries from the master you're retiring.

The discontinued units you pull out become spares for the sites you haven't reached yet. Spares get scarce once a product is discontinued. Power and Water Corporation, an Australian utility, noted in its business case for replacing end-of-support equipment that after end of support, "vendors do not sell spares or undertake repairs of faulty equipment."

How Long Does an RTU Swap Take, and How Do You Keep Site Visits Down?

Time at each site depends on how many cables move, how far the drive is and how many points you check before leaving, so we can't give a per-site figure that holds across networks. The number of trips is easier to control than the time on site. Aim for one trip to each site.

• Group sites by wiring. Sites that share a make, model and wiring style can share one kit design and one point map layout. A site wired differently gets its own point map and its own bench test before anyone travels to it.
• Collect missing documentation on trips you're already making. If a site's pinout or input types aren't written down, record them during routine maintenance, so the swap trip isn't spent working them out.
• Ship each kit complete. Send the RTU configured, with its adapter cabling and mounting hardware, so the technician has nothing to assemble or program at the site.
• Plan helicopter sites around flying weather. For sites you reach by helicopter, schedule the swap inside the weather windows when flights can go. Our guide to replacing alarm endpoints at remote mountain-top sites covers those sites in detail.

Hardware lead time sets the start of the whole rollout. A custom-engineered replacement typically has a field trial unit ready about two months from concept, and that's the unit you'd use for the bench test and pilot site. The custom-engineered replacement itself is typically delivered in approximately 90 days or less. A standard NetGuardian that already matches your sites ships sooner than a custom build.

What Does a Matched Replacement RTU Cost?

We don't charge non-recurring engineering (NRE) fees for a custom-engineered replacement when your order meets our minimum quantity of approximately 11 units. The unit price depends on the capacity and options your sites need, so we quote each project.

If you have discontinued RTUs at your sites, send us the make and model, photos of the connectors and whatever pinout documentation you have. We'll tell you what a matched replacement looks like and whether your existing cables can plug straight into it.

Talk to an Engineer | 800-693-0351

Andrew Erickson

Andrew Erickson is an Application Engineer at DPS Telecom, a manufacturer of semi-custom remote alarm monitoring systems based in Fresno, California. Andrew brings more than 19 years of experience building site monitoring solutions, developing intuitive user interfaces and documentation, and opt...