The 8-Step Checklist I Use Before Quoting or Commissioning a Siemens PLC

Who this checklist is for

If you're quoting, buying or commissioning a Siemens PLC — a LOGO! on a small conveyor, an S7-1200 on a packaging cell, or an S7-1500 line — this is the checklist I run before a quote goes out and again before a panel gets powered up. Eight steps. Roughly 25 minutes if you know where to click.

I've been handling automation procurement and commissioning orders since 2016. In that time I've personally made (and written down) 14 significant mistakes, worth somewhere around $18,000 in wasted budget and rework. Wrong memory cards. A firmware mismatch that ate a Friday afternoon. One backup-battery incident I'll get to in step 3. Now I maintain the checklist our team uses so nobody repeats my errors.

Skip the background if you want — the steps are below. But read step 8 before you send a price to anyone.

The steps

Step 1: Pin down the controller class before anyone says a number

The fastest way to waste money on a Siemens PLC is to let a price guide the spec instead of the other way around. Decide first: LOGO!, S7-1200, or S7-1500.

For context on the entry end — Siemens LOGO! PLC price for a base module (LOGO! 8, 8 or 12 I/O, 12/24V or 115/230V variants) sits roughly in the $150–$400 range depending on I/O count and version, and expansion modules add to that. Check the Siemens Industry Mall or your regional distributor for today's number, because it moves with the exchange rate and the distributor's own margin. I'm quoting a range I collected in the first quarter of 2025, give or take a few months.

The trap: LOGO! looks like a no-brainer on paper until you add three expansion modules, a power supply and the time to figure out its function block editor. At some point an S7-1200 starter kit is the cheaper system. I've made that mistake twice.

Step 2: Check local availability before you check global market share

A lot of procurement searches run something like "plc market share mexico siemens vs allen bradley." I get why — the number sounds like it should tell you which platform to standardise on.

It mostly doesn't. Global share figures shift depending on which analyst you read, and neither vendor is going anywhere. What actually decides your project is local: which distributor keeps spares on the shelf, which integrator your plant already trusts, and who can get you a replacement CPU before Monday. In Mexico specifically, both platforms have deep installed bases across different industries — check your own site's existing standard and your maintenance team's skill set before you let a market-share chart make the call.

Trust me on this one: I once standardised a cell on the platform I preferred instead of the one the plant's electricians were trained on. That decision cost us two weeks of support calls.

Step 3: Verify the 24V rail and the backup battery with a multimeter

This is the step most people skip, and it's the one that bites you six months later in the form of a CPU that loses its retentive memory after a power cut.

Here's how to check a battery with a multimeter, the way I do it on a panel:

• Open-circuit first. Multimeter on DC volts, appropriate range. Probe the cell without any load. A healthy 3.6V lithium backup cell should read close to its nominal value. A CR2032-style cell reading 2.9V is on its way out.
• Then under load. This is the part people miss. A cell that reads 3.2V on the bench and drops to 2.6V once it's actually doing work is dead — it just hasn't told you yet. Repeat the measurement with the battery in circuit and the CPU powered down.
• Check the rail, not just the battery. Siemens specifies a permissible 24V DC input range of roughly 20.4–28.8V on S7-1200/1500 modules (the exact figure is in the system manual for your specific module — check support.industry.siemens.com, don't take my word for the last decimal). A rail sitting at 19.8V under load is a red flag, and it's usually the power supply, not the battery.
• Log the reading and the date. Two columns in your maintenance sheet. Future you will be grateful.

I assumed a backup battery that looked new was new. Didn't verify. Turned out it had been sitting in a drawer since a previous project. The CPU dropped its retentions over a holiday shutdown and we spent the first morning of January re-entering parameters. That one was about $900 in labour and a lot of embarrassment.

Step 4: Lock the programming environment and licensing before delivery

For Siemens PLC programming, the question is never just "can I open the project" — it's "can I open the project with the version installed on this machine, with the licence this company actually owns."

Confirm three things: the TIA Portal version the project was written in, whether it opens in your installed version without an upgrade, and whether the licence covers the devices you're configuring. Siemens publishes the compatibility matrix online; check it rather than assuming. Then confirm the CPU firmware version matches what your project expects. A CPU shipped with newer firmware than your TIA Portal install supports is a bad afternoon.

Oh, and check who owns the software licence after handover. I should add that this comes up more often than you'd think on multi-contractor jobs.

Step 5: Build the full bill of materials, not the attractive one

The base CPU price is the least interesting number in the quote. What goes in alongside it:

• Memory card (if required for your CPU class)
• Connectors and terminal blocks — often sold separately
• 24V power supply, correctly sized with headroom
• Software licence and any runtime options
• Shielding, ferrules, DIN rail, wire duct
• Spare modules, and a spare of whatever fails most often on your line

I now calculate total cost before comparing any vendor quotes. The lower unit price with connectors and the card billed separately usually isn't lower at all.

Step 6: Plan battery and cell maintenance properly

If your panels, sensor packs or handheld test gear use rechargeable cells — 18650s are everywhere in the test kits we carry — sort out the charging gear before it becomes a problem. A dedicated charger that reports per-slot voltage is worth the money; a cheap single-slot unit that just lights up green tells you nothing. We keep a Nitecore battery charger on the bench for exactly this, because it shows the actual voltage per bay and we can log it against the cell.

The most frustrating part of cell maintenance: the same dead cells rotating back into service because nobody marks them. You'd think a red dot with a marker would solve it, but people forget. What finally helped was a simple bin system — charged, discharged, dead.

Step 7: Set the firmware and access protection on day one

Before the panel leaves the shop, set the protection level and record the password somewhere that isn't a sticky note on the inside of the door. Siemens positions its portfolio around IEC 62443 for industrial security, but the certification applies to how the system is configured and maintained — it doesn't protect a CPU left on the default access level. Also disable unused interfaces. It's a five-minute job at the bench and a nightmare to retrofit in the field.

Step 8: Run the total-cost math and write down your assumptions

Before the quote goes out, add up: hardware, shipping and import, software, engineering hours, commissioning hours, training, spares, and the cost of one likely rework. Then write down what you assumed — exchange rate, lead time, firmware version. When the quote comes back two months later and something has moved, you'll know exactly which line item to defend.

The $5,200 configuration that needed a $900 memory card and a $600 licence nobody quoted ended up costing more than the $6,400 all-inclusive option. I've been on both sides of that comparison.

Things that still catch people out

Two warnings, both from experience.

Don't trust a lead time you haven't confirmed in writing. "In stock" on a distributor portal and "on the loading dock" are different claims. Ask for the dispatch date in the order acknowledgement.

Don't assume "same specifications" means identical results across suppliers. I learned that one after ordering a batch of modules where each supplier interpreted "with connector" differently. Three weeks, two courier bills, done.

There's something satisfying about a commissioning that just powers up, the rail sits at 24.1V, the backup cell holds under load and the project opens without an upgrade prompt. After the battery incident, the firmware mess and the connector fiasco, getting all eight steps to land on the same day — that's the payoff. It's not glamorous. It's just repeatable.

If you're going to steal one step from this list, steal step 3. The multimeter is already in your bag.