Choosing a fixed ammonia detector for a poultry house

The question of how much ammonia is too much is covered in safe ammonia levels in a poultry house. This guide is about the instrument: what to look for on a fixed detector’s datasheet, what to ask the seller before it goes on your wall, and where to put it once it arrives.

Why a fixed detector and not a handheld

A handheld meter or a set of detector tubes gives you one reading, at one spot, at the moment you happen to be in the house. That has its uses. It is the easy way to take a reading at the birds’ head height, and it is a good cross-check on any fixed sensor.

What it cannot do is watch the house while you sleep. Ammonia builds on minimum ventilation through the night and falls when the fans pick up in the morning, so the reading you take on your round sees the end of the problem, not the middle of it. A fixed detector reads all night, every night, and the curve it leaves is the thing you adjust minimum ventilation against.

The two answer different questions, and they work well side by side.

Read the range and the accuracy together

Two lines on the datasheet matter more than the rest: the measuring range and the accuracy.

Accuracy on gas detectors is usually written as a percentage of full scale (FS). That means the error is a fixed number of ppm across the whole range, and it is the same size at 5 ppm as at 95 ppm. A detector built for an industrial ammonia plant with a range in the hundreds of ppm can be perfectly good at its job and still too coarse for a poultry house, where the limits that matter sit in the low tens.

So pick the range that covers your limit with room to spare, and no wider. Then check the resolution, the smallest step the display moves in, so you can see a slow rise before it becomes a fast one.

The GF-201 ammonia detector Henlytics uses reads 0-100 ppm with 0.1 ppm resolution and an accuracy of ≤±3% FS, which on that range means within 3 ppm. Other ranges are available on request, and for a poultry house the standard range is the one to ask for.

Ask about drift before you ask about anything else

Gas sensing cells drift over time. What matters is what the maker tells you to do about it. A seller who cannot answer these is selling you a number you will not be able to trust in a year:

• How often does it need calibrating, and with what? A real answer names an interval and a certified test gas.
• Who can do it, and how? On the farm, through a menu, or by sending the unit away.
• Can the sensing cell be replaced at the end of its life, or is the whole detector scrapped?
• What happens when the sensor fails? A detector that quietly reads zero after a cable is chewed is worse than no detector, because the screen looks fine.

For the GF-201, the datasheet answers all of it. It has automatic temperature compensation and zero and span drift correction. Calibration is done from the front-panel menu by trained personnel with certified gas, at least once every six months: a zero in clean air, then a span with ammonia near half of full scale applied for two to three minutes, then a check that the alarm outputs and readings still respond. The cell is replaced at the end of its life, and the inlet is kept free of dust between visits.

Check that it can live in a poultry house

A poultry house is warm, humid and dusty. Read the environmental lines on the datasheet with that in mind:

• Ingress protection. The GF-201 is rated IP65.
• Operating temperature. -20 to 50°C for the GF-201.
• Humidity. 10-95% RH, non-condensing. A detector is kept clear of splashing water, so it is mounted out of the line of wash-down hoses and away from spots that drip.
• Response time. How quickly the reading catches up with the air. The GF-201 ammonia detector is ≤30 seconds (T90).

Where it goes on the wall

The GF-201 datasheet sets the placement, and the ammonia levels guide uses the same rule:

• High on the wall, 0.3-0.6 m below the ceiling: ammonia is lighter than air.
• Above the birds’ reach.
• Near likely accumulation zones and ventilation dead spots.
• Away from air inlets and the fan end, so it reads house air rather than air coming in or going out.
• Clear of splashing water, dust jets and mechanical impact.

One thing to be straight about. Welfare limits such as the one in EU Council Directive 2007/43/EC are written for the level of the chickens’ heads, and a detector on the upper wall is not standing at that level. What the fixed detector gives you is a continuous, consistent record of the same air from the same spot, night after night, which is what tells you when the house is getting worse. If you need a figure at head height for an audit, take one with a handheld at bird level and note it next to the fixed reading at the same time. Over a few flocks you learn how the two compare in your own house.

Pair it with CO2, on its own detector

Ammonia rises when the litter gets wet and the air is not changing fast enough. CO2 rises when the air is not changing fast enough, full stop. Read together, they tell you whether you are looking at a litter problem or a ventilation problem. During brooding, with a closed and heated house, CO2 is the one to watch closely.

Each GF-201 carries one sensing cell for one gas, so CO2 is a second detector, the GF-201 CO2 unit, reading 0-5000 ppm. Both sit on the same RS485 cable back to the controller, each with its own address, and both readings land on the same chart for the house.

What the alarm thresholds mean

A detector usually has two kinds of alarm, and it helps to know which one you are setting.

The detector’s own relays. The GF-201 has a two-stage alarm, low and high, each on its own relay, and both levels are freely configurable. Those relays switch a local siren or light in the house. They work whether or not anything is connected upstream, which is exactly why they are worth wiring.

The alert that reaches your phone. That one is set per sensor in the dashboard. It is the one that gets someone out of bed, so it sits below the limit you work to, not on it, to leave the team time to raise ventilation first. What makes it useful at night is less the number than what happens after it fires: whether it repeats until someone answers, and whether you hear when the house has recovered. If the ammonia rises while the controller says the fans are on, check that they are actually turning: see what happens when ventilation fails.

How Henlytics measures it

Henlytics mounts a GF-201 ammonia detector high on the wall of each house, with a GF-201 CO2 detector and temperature and humidity sensors alongside. They connect over RS485 Modbus to a Genesis controller in the house, which reports over the cellular network to one dashboard for every house. You set the limits per sensor; alerts go to the phone of everyone on the farm account and repeat until someone acknowledges them, and a disconnected or shorted sensor shows as a fault rather than a number. It runs alongside your existing climate controller.

See ammonia and CO2 monitoring for the sensors and how they are installed.