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APC Measure-UPS II / AP9612 Environmental Management Card and Probe Exploration / Information

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APC's AP9612 SmartSlot accessory senses temperature and humidity through up to two attached probes, provides a low current regulated 12 volt output and four connections for dry contact switches or sensors that may be monitored by the card's logic. The temperature probes attach externally to the card and may be situated some distance away.

AP9612 Measure-UPS II Environmental Management Card and Accessories

The AP9612 does not operate by itself. Another SmartSlot device that can collect data gathered by the AP9612 must be present. AP9618 and AP9619 management cards utilize the same probes as the AP9612, although APC chose to omit the humidity sensor for some curious reason. (Both the AP9618 and AP9619 do support the gathering and display of humidity data if you use an AP9512TH or AP9512THBLK probe.) There is some suggestion based on APC "Smart" protocol reverse engineering and documentation that the data collected by a Measure-UPS board may be available over the UPS serial port to any interested software.

Despite being shown in the illustration above, the actual card (at least my example of it) does not have the power LED or reset button. There simply isn't room on the rear panel for either. Nor does there appear to be any provision for such functionality on the board. (Zooming into APC's illustration from the AP9612 user manual suggests that perhaps the "power" opening is not for an LED, but rather a connection point for power input. Why this would be needed is a total mystery, since the SmartSlot and external enclosures all provide power to installed accessories.)

I suspect the AP9612 is primarily intended to operate with the AP9606 Web/SMNP SmartSlot accessory, which will report on its presence and any sensor data via the web interface. I don't yet know if the early AP9605 SMNP-only SmartSlot accessory supports data retrieval from the AP9612 or not. If it does, it is only through SMNP reporting as no mention of the environmental monitor or its contact monitoring capability are shown in the telnet administration interface. An AP9617 card I tested was not initially capable of communicating with the AP9612. A little bit of prodding from the web management interface ("reset only lost environmental communication alarms") did get it working. Another person reports that this combination allows the use of up to three temperature/humidity sensors (on an AP9618 or 9619 board).

An 87C52 microcontroller oversees the AP9612 while an ADC0834 8-bit A/D converter digitizes all temperature and humidity input values. The A/D converter may also handle all dry contact monitoring duties.

APC's documentation for the AP9612 suggests that only one temperature/humidity probe is supported by the device, despite the presence of two probe connection points. Two probes are in fact supported by the AP9612 and return separate data feeds.

Since it seems that APC has purged some manuals for older products from their support web site, here is the owner's manual for the AP9612.

AP9512T / AP9512TH Probe Pinout (Female Socket)

NOTE: The pinout below is correct, though I still have no idea of pin 4's exact function.

If you have better information, please get in touch.

The following pinout assumes one is looking into the female connector on the AP9612 board itself.

6 Pin Mini DIN Connector (image credit: Wikipedia)
Pin Number
Function, Voltage or Signal
+ 12 VDC, Regulated
Common for Temperature/Humidity (both sensors read very high values with this pin disconnected)
No Connection

An LM358 dual operational amplifier integrated circuit likely serves to boost signals from both the temperature and humidity sensors inside the probe, presumably to offset the effect of cable loss on the miniscule signals returned by each sensor. Hence the requirement for a power source leading to the probe. Temperature is sensed by a thermistor in all probes. Humidity is sensed by a TDK CHS-UGR device. All temperature-only probes that I have so far seen include the empty spaces for humidity sensing capability as well and could probably be modified.


My card dates from early 2002 or so and came with firmware version 4Sx. A sticker on the microcontroller bears a copyright from the year 2000 and indicates a checksum value of 20AD. No upgrades are possible short of replacing the 87C52 microcontroller, as it is a one time programmable part.

Since writing this, I've found an older AP9612 card (made in the 36th week of 1997) having firmware revision 4Jx, checksum 0FD9 and a copyright of 1995. Despite this earlier card having its second environmental monitor port covered over and marked as "RESERVED FOR FUTURE USE", the second port works just fine.

Seen but not yet proven to exist (!!) is a "4Kx" firmware revision.

If you know of other firmware releases for the AP9612 or what each release changes, please contact me!

Cable Extension

I've found that a male/female six pin mini-DIN extension cable (sold for extending the connection between a PS/2 keyboard and a computer) fifty feet in length works perfectly well. I don't know how much further than that you could go.


One of my cards reports temperatures (and, as best I remember) humidity data readings that are about twenty degrees/percent too high. The probes work correctly with other AP9612 and AP9618/19 boards. I'm not sure what the cause is. I suspect a passive component has drifted out of acceptable tolerances.

Hardware Revisions

Of the two boards I have, serial numbers JA0217013591 and WA9736128411, the later board is marked as 640-0810D Revision 4 and bears a 1998 copyright. The earlier board has a 1995 copyright and is marked as 640-0810B Revision 2. Both boards appear identical apart from different passive component values in certain positions.

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AP9612TH card, manual and accessories image copyright American Power Conversion Corporation and Schneider Electric. Use of this image and provision of the manual at no cost to rightful owners of the AP9612 hardware is believed to fall under the fair use doctrine within United States copyright law, where exceptions may be made for educational, news reporting, critical commentary and certain other uses that normally might constute infringement. I am not, however, a lawyer and this is not legal advice.

Mini-DIN port image sourced from Wikipedia, original here.
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