A historian for forty tags
You have one machine, or one line, or a boiler house. You want the last few months of temperatures and motor currents somewhere you can look at them when something goes wrong. You ask what a historian costs and the first quote has a comma in it.
That is not because you asked badly. It is because the smallest tag-metered package anyone sells is 3,500 tags, and you are below the minimum order quantity. The products with no tag limit exist — they just all want a server from you.
Last updated
The floor, in numbers
The three smallest packages sold by the tag, read from each vendor's own pricing page on 2026-08-11. Full table — including the products that are not metered by tag — and the method on what a data historian actually costs.
| Smallest tag-metered package | Tags | Price | Source |
|---|---|---|---|
| Canary Private Cloud, Extra Small | 3,500 | ≈ $1,027 / month | canarylabs.com/pricing |
| TDengine Cloud, Starter | 5,000 | $970 / month | tdengine.com/pricing |
| Canary On-premise subscription | 3,500 | $250 / month | canarylabs.com/pricing |
A single packaged machine is usually twenty to eighty signals worth historising: a few temperatures and pressures, motor currents, run states, a counter or two, some setpoints. A small plant with several machines and a boiler house is comfortably inside the low hundreds.
So the entry-level metered product is somewhere between forty and a hundred times what you need, and it is priced accordingly. You are not being quoted enterprise money because your problem is hard. You are being quoted enterprise money because nobody has built the small size — the alternative on offer is not a smaller package, it is an unmetered one you host yourself, which is the next section.
What people actually do instead
1. Nothing — the PLC keeps its own trends
Worth naming first because it is what most small sites do. The HMI has trend screens, the drive keeps a fault buffer, and when something breaks you look at the last few hours.
This is fine until the question is comparative — “is this bearing running hotter than it did in the spring?” — because that needs data from before you started wondering. The cost of doing nothing is invisible right up until the first time you need last year.
2. Free software on a spare PC
Entirely legitimate, and the licence really is zero. Timebase is free with no tag limit, TDengine is free self-hosted up to 5,000 tags, and InfluxDB OSS is free. Add Grafana and you have a historian with dashboards for the price of a machine.
3. Hosted, at the small end
This is what we sell, so weigh it accordingly. Business is €89 a month for 500 tags; Pro is €9 for 50; the free plan is 5 tags and costs nothing, which is enough to prove the plumbing with a real PLC before spending anything.
Full resolution is 6 months on Pro and 2 years on Business, and the hourly minimum, maximum, average and count for every tag is kept 10 years on every plan — so the “is it running hotter than last spring” question stays answerable long after the detail has gone. See how long data is kept.
Ingestion is OPC UA or MQTT through a collector container you run on the plant network. It connects outward only — no port forwarding, no inbound firewall rule, no PLC exposed to the internet. That constraint is the first thing a controls engineer asks about and the reason the design is shaped this way.
You do not need SCADA to have a historian
A recurring blocker: the historian is sold as a module of a SCADA platform, so it looks like you need the platform. You do not. A historian needs values and timestamps. If your PLC has an OPC UA server — most do now — or anything on the network can publish MQTT, that is sufficient.
Supervisory control is a genuinely separate product and a genuinely large purchase. If what you want is “keep the numbers and tell me when one goes out of range”, buying a SCADA platform to get it is buying a car for the radio.
When we are the wrong answer
- Above 500 tags. That is the ceiling on the largest published plan. If you are at a thousand signals and growing, you have crossed into the range the established vendors are built for, and their smallest package finally fits.
- Data must not leave the site. Some plants have that rule and it is not negotiable. There is no on-premise install here. Timebase is free and runs where you put it.
- You need browse-and-select over the OPC UA address space. Every NodeId is typed by hand here. At forty tags that is twenty minutes and it usefully caps what you can accidentally subscribe to. At two thousand it is the wrong tool.
- You need a contractual uptime SLA. The self-service plans have none.
- You need control, alarming on the plant floor, or an HMI. Not what this is.
How to decide, in three questions
- Count the signals you would genuinely look at a year from now. Not everything the PLC exposes — the ones you would open a trend on during a breakdown. Almost everyone overestimates this by a factor of five.
- Ask who restores the backup. If there is a name, self-hosted free software is excellent and you should use it. If there is no name, you are choosing between hosted storage and eventually losing the data.
- Ask whether the data needs to survive the site. A historian in the switchroom shares a fate with the switchroom.
The free plan exists for exactly this decision: 5 tags is enough to point a collector at a real PLC, watch real values arrive, and find out whether any of this is worth paying for — before paying for it.
Common questions
- What is the smallest data historian you can buy?
- If it is metered by tag, 3,500. Canary’s smallest on-premise and Private Cloud packages are both 3,500 tags and TDengine Cloud’s Starter plan is 5,000, and none of them sells a smaller size — which is why a site with forty signals finds nothing that fits. The way out is a product that is not metered by tag at all: Ignition’s Industrial Historian suite is a $3,500 perpetual licence with no tag limit, and Timebase is free with none either. Both want a server from you.
- How many tags does one machine actually have?
- For a single packaged machine, typically twenty to eighty signals worth historising — a handful of temperatures and pressures, a few motor currents, run states, counters and setpoints. A small plant with several machines and a boiler house is usually in the low hundreds.
- Can I log PLC data without a SCADA system?
- Yes. A historian only needs values and timestamps. An OPC UA client, an MQTT publisher or an HTTP POST is enough — supervisory control is a separate product that you may not need at all if what you want is history and alerts.
- Is free historian software good enough for a small plant?
- Often yes, on licence cost. Timebase is free with no tag limit and TDengine is free self-hosted up to 5,000 tags. The real question is whether you have somewhere to run it that stays up, gets patched, and has a backup someone has actually restored from.