McNab Model AP-IH pH Analyzer

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Model AP-IH is an industrial analyzer which may be supplied to measure pH, conductivity or resistivity. Used for indicating as well as controlling (via its internal PID controller) to dose pH to the desired levels. When measuring conductivity, it features McNab's patented automatic self-zero-correction.


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The basic application of the AP-IH Analyzer is that of pH (hydrogen-ion concentration) or ORP (oxygen reduction potential) measurements.


The AP-IH is designed to provide an indication of a solution's pH and with an appropriate signal/output module to provide control signal or alarm action. The operation range of the glass-based system is 0 to 14 pH and 2-10 for the antimony-based system. The ORP Range is from -1999mv to +1999mv.


The AP-IH system physically consists of two elements: The analyzer electronics case, and a probe. The typical probe transmitter is not required on this "driven shield" patented design.

A86-50_600.jpg (28797 bytes)The "Analyzer" contains the main circuit board, signal preamplifier, indicators and meter. The main circuit board (hereafter referred to as the mother board) is mounted to the back wall of the case. This board contains the regulated power supply, the instrument fuse, an alarm circuit, an analog, non-isolated, 4-20 mA DC output, and the interconnection terminal blocks. A second module, preamplifer, is mounted to this motherboard. A signal/output controller module is optional. The signal output controller module provides signal or control output.

The remaining components of the AP-IH Analyzer are the meter, the panel indicator lamps and the power switch all mounted on the swingout door of the case assembly. Cables and connectors are provided to interconnect the motherboard with the front panel components and the preamplifier module with the probe. The cabinet is a steel NEMA-12 (or optional NEMA-4 or NEMA 4X) enclosure, and is designed for wall or pipe mounting. A gasket is provided between the door and cabinet. The door is secured by a hinge and a holding screw. Refer to drawing 18493. A female connector for the probe maybe located on the case assembly bottom or the probe maybe directly connected to the preamplifier terminal block (see probe drawing). Also on the bottom are conduit knockouts with 7/8 inch diameter access.

A86-38_600.jpg (17131 bytes)The pH probes used with the AP-IH Analyzer system are either glass, solid state Antimony or ceramic type. The combination glass electrode is factory prefilled and sealed and does not require refilling. The solid state Antimony probe has an antimony sensing electrode and a ceramic epoxy reference electrode. The solid-state probe is all ceramic and is of a more rugged construction.

Two probes styles, (1) screw-in MP-22 glass-based pH system [MP-6 with connector], MP-41 antimony-based pH system [MP-39 with connector], MP-16 ORP or (2) valve-inserted MP-24 glass-based pH system [MP-40 pH with connector, MP-15 ORP], are available. The screw-in probe has a one-inch NPT screw thread and mounts into a tee or tank wall fitting. The valve-inserted probes are designed to insert coaxially into a McNab insertion valve.

In cases where the plant's high pressure requirements do not permit easy probe withdrawal for maintenance, or where short dead-time demands good full in-line sampling flows, a valve-inserted probe system, L-3p, should be used. This is known also as an injector probe assembly or hot tap valve. It also has a mechanical interlock which prevents extracting the probe until the L-3p valve is closed (as required by OSHA for certain piping applications).


The model AP-IH has various preamp modules which set the meter scale and the type of probe to be used with unit and, optionally, there is a signal/output module and it has various configurations: 4-20 isolated, On/Off dual controller, and proportional dual controller. The configuration code will specify which different types of PC boards are actually used in the unit.

The antimony probe is not compatible to the digital meter in that it is somewhat not linear in its output to pH input and, hence, it is offered only with an analog meter. The digital meter because of its resolution is supplied with the full range glass-based pH preamplifier module (0-14 pH PN 18478-G3) or ORP preamplifier as the case requires.


View probe specifications for the AP-I family of McNab analyzers.

820-03 Modified

383-2 East 29th Street | Buena Vista, VA | USA 24416-1293

540.261.1045 voice | 540.261.1268 fax |

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