Question 1

What is the difference between Option 1S2 and Option 2S2?

Accepted Answer

Option 1S2 includes one SPDT reed switch, adjustable from 30% to 90% of full scale. It is typically used for low flow protection — shutting down equipment when flow drops below a safe threshold. Option 2S2 includes two independent SPDT reed switches, each separately adjustable over the same 30–90% range. This allows you to set both a low flow alarm and a high flow alarm simultaneously on a single meter.

Question 2

Which products are compatible with the limit switch options?

Accepted Answer

Reed switch options (1S2 and 2S2) are available on most Flo-Gage product lines. They are not compatible with meters already equipped with Options K, N, W, W2, W3, X, Y, or Z. If you need both a transmitter and a switch, contact Northeast Controls to discuss available combinations.

Question 3

What is Option IS and when do I need it?

Accepted Answer

Option IS is the intrinsically safe version of the limit switch, required for installations in classified hazardous locations (Class I, Division 1). It is CSA and ATEX approved. Option IS-LED adds LED indicators for at-a-glance status viewing and easier field calibration. If your installation is in a hazardous area, always specify Option IS or IS-LED.

Question 4

Can I use a limit switch for pump control or safety interlocks?

Accepted Answer

Yes. The SPDT (single pole double throw) contacts on both 1S2 and 2S2 can be wired for either normally open (N.O.) or normally closed (N.C.) operation, making them well-suited for pump start/stop control, safety interlock circuits, and alarm relay triggering. The 3-watt contact rating is sufficient for most relay and PLC input circuits.

Question 5

What are the electrical ratings for the reed switches?

Accepted Answer

The reed switches are rated at 3 watts maximum contact power, with a maximum switching current of 250 mA and a carry current of 1.0 Amp. Maximum voltage is 175 Vdc or 245 Vac. These ratings are suitable for most relay coils, PLC digital inputs, and low-power alarm circuits. Do not use the switches to directly switch high-current loads.

Question 6

What is the setpoint accuracy and repeatability?

Accepted Answer

Setability (the precision with which you can set the trip point) is ±5% of full scale. Repeatability — how consistently the switch trips at the same flow rate after repeated cycles — is ±1% of full scale. Hysteresis (the difference between the trip and reset points) is 7 to 13% of full scale. This hysteresis prevents rapid on/off cycling near the setpoint.

Question 7

Over what range can the setpoint be adjusted?

Accepted Answer

The setpoint can be adjusted from 30% to 90% of the meter's full scale flow range. Setpoints below 30% or above 90% of full scale are not achievable with the standard reed switch design. If you need a setpoint outside this range, contact Northeast Controls to discuss alternative solutions.

Question 8

Are the switches sealed against the process fluid?

Accepted Answer

Yes. The reed switches are hermetically sealed in glass and epoxy-potted, providing excellent protection against moisture and contamination. They are located inside the meter body and accessed by removing the back cover. The sensing mechanism is magnetic — the switch detects the position of a magnet on the pointer — so there is no physical contact with the process fluid.

Question 9

What conduit size is used for the switch wiring?

Accepted Answer

The conduit entrance is ½″. Standard electrical conduit fittings for ½″ trade size are compatible. For hazardous location installations (Option IS), use conduit seals and fittings rated for the applicable hazardous area classification.

Question 10

How do I wire the SPDT contacts?

Accepted Answer

Each reed switch has three terminals: Common (C), Normally Open (N.O.), and Normally Closed (N.C.). For a low flow alarm that activates when flow drops below the setpoint, wire your load between C and N.C. — the circuit will open when flow falls below the trip point. For a circuit that activates on low flow, wire between C and N.O. Refer to the wiring diagram on the data sheet for your specific meter series.

Question 11

Do I need to zero the meter before adjusting the switch setpoint?

Accepted Answer

Yes — this is the first step in the adjustment procedure. Verify and correct the meter zero (using the coarse or fine zero procedure) before setting the switch. An incorrect zero will shift the actual trip point away from your intended setpoint, reducing accuracy.

Setability	±5% F.S.
Repeatability	±1% F.S.
Hysteresis	7 to 13% F.S.
Contact Rating	3 watts
Voltage (max)	175 Vdc / 245 Vac
Current (switching)	250 mA max
Current (carry)	1.0 Amp max
Adjustment Range	30% to 90% of full scale
Option 1S2	1 Reed Switch with SPDT
Option 2S2	2 Reed Switches with SPDT
Conduit Entrance	½″
Approvals	CSA and ATEX (intrinsically safe option)

Flow Meter Limit Switches

Overview

Switch Options

Option 1S2 — Single Reed Switch

Option 2S2 — Dual Reed Switches

Specifications

Applications

Adjustment Procedure

Limit Switch FAQ

Choosing the Right Option

Specifications & Ratings

Installation & Wiring

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