Ashcroft Flow Meters, Pressure Transducers, and Sensor Specs: A Purchasing FAQ

I'm the office administrator for a 60-person industrial automation and calibration company. I handle the instrument purchasing—about $180,000 a year across 12 vendors—and I report to both operations and finance. When I took over purchasing in 2022, I had to learn the hard way what happens when you order sensor specs from memory instead of the datasheet.

This FAQ covers the questions I hear most from our team and customers. If you're sourcing pressure or flow instruments, these will save you from my mistakes. Plus one question you didn't know to ask: does Cognex use Sony sensors?

• What's the difference between an Ashcroft water flow meter and an Ashcroft differential pressure transducer?
• For an inductive proximity sensor M30 x 1.5, what specs really matter?
• Static pressure sensor or differential pressure transducer: which one do I order?
• Does Cognex use Sony sensors?
• Why do replacement sensor specs always seem to change?
• Can I use an Ashcroft transmitter with the PLC we already have?

What's the difference between an Ashcroft water flow meter and an Ashcroft differential pressure transducer?

An Ashcroft water flow meter measures flow directly. Think of it as a standalone device: water goes through it, and you get a reading in GPM or liters per minute. A differential pressure transducer measures the pressure difference between two points. That difference can be converted to flow if it's installed across an orifice plate, venturi, or a primary flow element.

So the quick answer: if you need a direct flow reading, order the flow meter. If you already have a primary element or need to monitor filter pressure drop, order the differential pressure transducer. Buying a DP transmitter and assuming it will output GPM by itself is a mistake I made once. It gives you pressure difference until you configure the flow calculation somewhere downstream.

For an inductive proximity sensor M30 x 1.5, what specs matter most?

The M30 x 1.5 is just the mounting thread. It tells you the sensor will screw into a 30 mm hole with a 1.5 mm pitch. It does not tell you whether the sensor will actually work in your machine.

These are the specs I now check before ordering:

• Output type: PNP or NPN. Get this wrong and you'll have a sensor that never triggers the PLC input.
• Normally open vs normally closed. A sensor with the wrong fail-safe state can cause a dangerous false machine start.
• Shielded vs unshielded. This changes detection range and how much metal can be around the sensing face.
• Supply voltage: 10-30 VDC is common, but always confirm.
• Rated sensing distance and target material. Steel is the reference; aluminum and plastic respond differently.

I still kick myself for ordering a batch of M30 sensors by thread size alone. The part looked right from the outside, but the output was wrong. That mistake cost about $350 in expedite fees plus a half-day of downtime.

Static pressure sensor vs differential pressure transducer: which one do I actually need?

A static pressure sensor measures pressure at a single point. It's usually referenced to atmosphere, so it tells you the gauge pressure in a pipe or tank. A differential pressure transducer has two ports and measures the difference between them. They are not interchangeable.

Use a static pressure sensor for:

• Checking supply line pressure
• Monitoring compressor discharge pressure
• Ensuring a tank stays within its rated pressure

Use a differential pressure transducer for:

• Filter monitoring
• Level measurement in a vented tank
• Flow measurement across an orifice plate

If you've got a vented tank with a transmitter at the bottom, a static sensor can give you level. But if you need to know the difference between two pressures, don't let anyone sell you a static sensor and say it's basically the same. It's not.

Does Cognex use Sony sensors?

This one comes up because someone on our floor found a vision camera with a Sony image sensor and assumed every Cognex camera uses the same one. That's not a safe assumption.

Some Cognex vision cameras have used sensors from Sony. Sony makes a lot of industrial CMOS image sensors, and they show up in machine vision cameras across many brands. Whether a specific Cognex model uses Sony depends on the model, the generation, and sometimes the revision.

Honestly, I'm not sure why every manufacturer doesn't just state the sensor brand clearly on the spec sheet. My best guess is that sensor suppliers revise components, and the camera part number stays the same. If you need a direct answer for a particular model, the only reliable source is the official spec sheet or a direct inquiry to Cognex.

As a buyer, what matters more is resolution, interface, trigger, and lens mount. Those are what make a camera functionally compatible with your machine.

Why do replacement sensor specs always seem to change?

Replacement part numbers are not as stable as we'd like. Manufacturers refine a product line, merge part numbers, or discontinue an old option and replace it with a newer version. In 2024, we consolidated vendors and had to re-qualify three product families because parts we'd ordered for years were no longer offered.

The fundamentals haven't changed. Range, output signal, and process connection are still what you need to get right. But part numbers and options have a way of shifting, which is why I always ask for the current datasheet before reordering.

What I've learned:

• Always request the current datasheet before ordering.
• Keep old datasheets as a PDF, not just a bookmark. Part numbers change when websites change.
• If you're using an Ashcroft product, identify the exact model code from the label, not from an old PO.

In one case, we had a communication failure with a supplier. We both said 'standard configuration' but meant different things. We discovered it when the transmitter arrived with a 0-10 VDC output instead of 4-20 mA. That order also came with the wrong invoice, which finance rejected. The part was replaced, but the paperwork took longer than the hardware.

Can I use an Ashcroft transmitter with the PLC we already have?

In most cases, yes. Ashcroft makes pressure transducers and differential pressure transmitters with common industrial outputs, so they integrate with standard PLC analog input cards. The catch is that you have to match the electrical interface, not just the pressure range.

Before I order anything, I check three things:

• Analog output: 4-20 mA vs 0-10 VDC. These are not interchangeable without a signal converter.
• Wiring configuration: 2-wire loop powered vs 3-wire. This affects the terminal block and the power supply.
• Process connection: NPT, BSPP, or flange. I learned this one the hard way when a new Ashcroft instrument arrived with the right range but the wrong thread. The adapter added cost and, more importantly, delay.

If the specs match, the transmitter doesn't care what brand the PLC is. The analog input just reads the current or voltage.