Analog vs Digital (Multifunction) Timing Relays
What is the difference between an analog and a digital timing relay? An analog (dial-set) timing relay sets one delay function on a single potentiometer scale, while a digital multifunction timing relay selects from several functions and several timing ranges on DIP or rotary switches, sometimes with a digital display, per IEC 61812. That extra selection logic lets one digital part replace three to six single-function analog parts in a panel, at the cost of a slightly more deliberate setup procedure. This article compares setting method, function and range coverage, repeat accuracy and drift, and panel-stock economics, and covers when a fixed single-function timer still beats a multifunction one.
What Counts as an "Analog" Timing Relay
On the shop floor, "analog" means a timer set with one continuous dial or a single potentiometer, covering one function and one fixed range. Schneider's Zelio Time RE17 and ABB's CT-ERD (on-delay) and CT-AHD (off-delay) are typical examples: 17.5 mm modular, a scale you turn to a time value, no function selector because the function is fixed at the factory. The circuit inside is electronic, not literally analog in the strict signal-processing sense, but the interface is a continuous scale rather than a digital selector — that's the distinction that matters on a panel drawing.
The lineage goes back further. Pneumatic (air-bleed) and small motor-driven timers were the original "analog" devices — no electronics at all, just a bellows or a synchronous motor and a cam. Some panel builders still use pneumatic timers on older machine retrofits, but new designs default to electronic dial-set units for repeatability and smaller footprint.
What Counts as a "Digital" (Multifunction) Timing Relay
A digital multifunction timer, such as Schneider's RE22 or ABB's CT-MFD, replaces the single dial with three separate settings: a DIP switch or rotary selector for the function (on-delay, off-delay, star-delta, flasher, and more on one part), a rotary switch for the timing range (for example 0.1 s to 100 h across several decade steps), and a potentiometer or thumbwheel for the value within that range. Many models add an LED to show which range is active. The multifunction and multi-range timing relays family covers this in more depth, including how the range-and-function combination is read off the housing.
Multi-voltage supply input is common on this class — one part accepts, say, 12-240 V AC/DC — which further cuts the number of distinct catalogue numbers a panel shop has to carry. That's the core trade a digital multifunction timer is built around: more setup steps per unit, fewer distinct units on the shelf.
Setting Method: One Scale vs Function + Range + Value
Setting an analog dial-set unit is a single action: turn the knob to the marked time. Setting a digital multifunction unit is three actions in sequence — pick the function, pick the range, then dial the value inside that range — and getting any one of the three wrong gives a timer that runs, just not to the delay the panel builder intended.
What we see in the field: a multifunction timer left on its factory-default function (often on-delay) because only the range and value were checked against the drawing, not the function switch. The fix is procedural, not technical — check all three settings against the wiring diagram, not just the time value — but it's a real source of commissioning callbacks that a single-function analog timer, with only one thing to set, doesn't produce.
Function and Timing-Range Coverage
An analog single-function timer covers exactly one job: an on-delay timing relay only delays on, an off-delay timing relay only delays off, and its range is fixed at the factory, commonly something like 0.1 s to 10 s or 1 s to 100 s depending on the catalogue variant ordered. Swap the application and you swap the part.
A digital multifunction timer collapses on-delay, off-delay, star-delta, single-shot, and cyclic/flasher functions, plus several decade ranges, into one part number. That single part can also serve a star-delta motor starting job on Monday and an on-delay interlock on Tuesday, without a stores trip. The trade-off is that the multifunction unit's per-function timing behavior has to be verified in the datasheet's function table rather than assumed from the part name.
Repeat Accuracy and Long-Term Drift
Both classes are rated the same way under IEC 61812: repeat accuracy as a percentage of the set value, plus a separate setting accuracy for how close the dial position tracks the marked scale. A typical repeat accuracy band on either analog or digital electronic timers runs in the low single-digit percent of set value; the number to check on the datasheet, not assume.
Formula: Repeat accuracy error — Source: IEC 61812
Δt = ± a% × tset
| Symbol | Description | Unit |
|---|---|---|
| Δt | Maximum deviation between successive timing cycles at a fixed set value | s (or ms/h as applicable) |
| a | Repeat accuracy rating from the datasheet | % of set value |
| tset | Time value the dial or digital selector is set to | s (or ms/h as applicable) |
Where the two classes tend to differ, in practice, is where in the range the set value sits. On an analog dial with one fixed range, the working point is usually mid-scale, where mechanical readability and repeat accuracy are both best. On a digital multi-range unit, the same absolute delay might land near the bottom of one range or the top of the next range down — this depends on which decade range was selected — and accuracy at the extreme ends of a range is typically the worst case on the datasheet, not the typical case. Read the accuracy figure at the range you'll actually use, not the headline number. More on this in timing ranges and accuracy specs.
Panel Stock, Cost and Spares Trade-offs
Per unit, a single-function analog timer is usually the cheaper part. Multiply that by the number of distinct function/range combinations a panel shop needs to stock, though, and the comparison flips: five or six analog SKUs at a lower unit price can cost more in total carrying cost, counting, and stockout risk than one or two multifunction digital SKUs that cover the same ground.
Spares strategy follows the same logic. A single multifunction unit in the spares bin can stand in for several different analog part numbers in an emergency, provided someone sets the function and range correctly on install — the commissioning discipline from the earlier section applies directly here. A timing relay selection decision at the design stage should weigh this against the raw unit-price comparison, not just the line-item cost on a BOM.
Choosing Between Analog and Digital: A Side-by-Side View
| Criteria | Analog (dial-set, single-function) | Digital (multifunction, multi-range) | Legacy pneumatic/motor-driven |
|---|---|---|---|
| Setting steps | One dial, one range | Function + range + value | One adjustable air-bleed/cam |
| Function coverage | Fixed at the factory | Several functions in one part | Fixed, mechanical |
| Timing range coverage | One fixed range per part | Several decade ranges per part | One mechanical range |
| Typical panel role | Single, repeatable job (e.g. one on-delay interlock) | Mixed job panels, spares consolidation | Older machine retrofits only |
| Commissioning risk | Low — one setting to verify | Higher — three settings to verify against the drawing | Wear-dependent, drifts with age |
For a panel with one recurring delay job across many builds, the single-function analog timer stays the simpler and cheaper choice, largely because there's nothing to misconfigure beyond the one dial. For a spares bin, a prototype run, or a machine that needs several different delay behaviors across its lifecycle, the digital multifunction timer pays for its extra setup complexity through fewer stocked part numbers. See the timing and control relays range for both classes stocked side by side, and the timing relay engineering guide for how this fits the wider function and standards picture.
Frequently Asked Questions
Is a dial-set electronic timer really "analog"?
The internal circuit is electronic, not analog in the strict signal sense, but the interface — one continuous potentiometer scale, one fixed function — is what earns it the "analog" label on a panel drawing, as opposed to a digital multi-selector timer.
Are digital multifunction timing relays more accurate than analog dial-set units?
Not automatically. Both classes are rated to a repeat accuracy percentage of set value under IEC 61812; the number depends on the specific model and, for multi-range digital units, where the set value falls within the selected range.
Can one digital multifunction timer replace several analog timers in a panel?
Yes, provided the required functions and ranges are all covered by that part's function table. Verify each application against the datasheet rather than assuming full coverage.
Does a digital timing relay need a numeric display to be called "digital"?
No. The defining feature is DIP/rotary selection of function and range rather than a single continuous dial; a numeric or LED display is a common addition, not a requirement of the category.
Which type is cheaper to stock, analog or digital multifunction timers?
Per unit, analog single-function timers are usually cheaper. Across a full set of function/range combinations, a smaller number of multifunction digital SKUs can carry a lower total stocking cost — compare the whole family, not one part number.
Do star-delta timing relays come in both analog and digital form?
Yes. Dedicated single-function star-delta timers (e.g. ABB CT-VWD/CT-YDD, CT-SDD) set run-up and transition time on fixed scales; multifunction units like RE22R or CT-MFD offer star-delta as one selectable function among several. See star-delta timing relays for motor starting for the wiring and transition-time detail.
Conclusion
Analog and digital multifunction timing relays solve the same problem — a set delay between trigger and output change — with a different trade between setup simplicity and part-count flexibility. A single-function dial-set timer has one thing to set and one thing to get wrong; a multifunction digital timer has three settings and covers several jobs from one stocked part. Pick based on how many distinct delay behaviors the panel family actually needs, not on unit price alone.
