A&D GP-20K Manual, Explained: Setup, Calibration, Counting and Error Codes

This GP-20K manual guide covers setup, one-touch calibration, counting and error codes for the A&D GP-20K washdown balance (21 kg x 0.1 g), on sale for $2,599.00 (regular $4,206.00), in stock.

A&D now lists the GP-20K as out of stock, and the GX-22001L is the current alternative.

The A&D GP-20K is a 21 kg x 0.1 g high-capacity balance with a 384 x 344 mm pan, an IP65 dust-tight and water-jet-protected body, a built-in calibration mass and A&D’s Super Hybrid Sensor. A&D writes one instruction manual for the whole GP series, from the GP-12K to the GP-102K, so GP-20K owners have to pick their numbers out of shared tables. Below are the GP-20K figures from that manual, with the key names and display messages as the balance shows them.

GP-20K manual at a glance: specifications

Item	GP-20K
Capacity x readability	21 kg x 0.1 g (maximum display 21.0084 kg)
Repeatability (standard deviation)	0.1 g
Linearity	±0.2 g
Accuracy right after internal-mass calibration	±1.0 g at capacity, in good conditions (10 to 30 °C, no drafts)
Sensitivity drift	±3 ppm per °C (10 to 30 °C, automatic self calibration off)
Stabilization time	About 1.5 seconds at FAST
Counting	Samples of 10, 25, 50 or 100 pieces; minimum unit weight 0.1 g
Percent mode	Minimum 100 percent reference 10 g
Calibration	Internal mass plus external: built-in mass (one-touch CAL key and automatic self calibration), plus external calibration with a 10 kg or 20 kg weight
Interface	RS-232C with A&D’s WinCT Windows software
Protection and sensor	Complies with IP65; Super Hybrid Sensor (SHS)
Pan, size and weight	384 x 344 mm (15.1 x 13.5 in) pan; 372 x 615 x 130 mm body; about 17 kg
Power	AC adapter, about 14 VA; the AD-1682 rechargeable battery is an optional add-on, not included
Operating range	5 to 40 °C (41 to 104 °F), 85 percent relative humidity or less, no condensation

Setting up the GP-20K

1. Check the box: balance, pan, AC adapter, reference card and instruction manual. The under-hook, printer, RS-232C cable, comparator or analog output board, battery and calibration weights are not included unless ordered. Keep the box and foam for mail-in service.
2. Pick the spot: a solid table, as level as possible, away from direct sun, heaters, air conditioners, motors and magnets. A&D’s best conditions are about 20 °C (68 °F) at about 50 percent relative humidity, and ground-floor corners shake least.
3. Level it: turn the leveling feet until the bubble in the spirit level is centered, and set the swing-arm display where operators can read it.
4. Check the adapter: confirm the AC adapter type matches your outlet, then plug it in.
5. Warm it up: at least 30 minutes with nothing on the pan for daily use. After the first install or a move, A&D calls for at least 12 hours so the balance reaches room temperature, then a calibration before use.
6. Calibrate with the CAL key; the steps are in the GP-20K calibration section below.

Keys and the function table

Key	When weighing	Hold the key
ON:OFF	Display on or off (standby)	–
SAMPLE	Starts sample storing in pcs or percent	Opens the function table (ba5fnc)
MODE	Steps through the stored units, pcs and percent	Response adjustment and self check (RESPONSE)
CAL	One-touch calibration with the built-in mass	External-weight calibration (Calout) and calibration test (CCout)
PRINT	Sends the reading to a printer or PC, or stores it in data memory	–
RE-ZERO	Zeroes the display or tares a container	–

In the function table, SAMPLE steps to the next item, RE-ZERO changes the value, PRINT stores it and CAL exits. Settings you will use most are Cond (response), Unit (stored units), dout (data output and GLP report) and data (data memory). Five function switches can lock calibration and interface settings so a second shift cannot change them by accident.

Weighing units on the GP-20K

Unit	Display	GP-20K capacity x readability
Gram	g	21000.0 x 0.1 g
Kilogram	kg	21.0000 x 0.0001 kg
Ounce (avoir)	oz	740.755 x 0.005 oz
Pound	lb	46.2970 x 0.0005 lb
Pound-ounce	L oz	46 lb 4.75 oz x 0.01 oz
Troy ounce	ozt	675.165 x 0.005 ozt
Metric carat	ct	105000.0 x 0.5 ct
Momme	mom	5600.00 x 0.05 mom
Pennyweight	dwt	13503.3 x 0.1 dwt

Store only the units you use: hold SAMPLE until ba5fnc shows, press SAMPLE until Unit appears and press PRINT. Press SAMPLE to step to a unit and RE-ZERO to select it; press PRINT to store the list and CAL to return to weighing. MODE then steps through only the units you stored.

Counting parts on the GP-20K

1. Press MODE until pcs shows, then press SAMPLE.
2. Press SAMPLE again to choose 10, 25, 50 or 100 pieces.
3. Set a bin or tray on the pan if you use one and press RE-ZERO.
4. Count that many pieces onto the pan and press PRINT to store the unit weight.
5. Load the parts to count and read the piece count.

• The smallest unit weight on the GP-20K is 0.1 g, so washers, fasteners, labels and molded parts count well in a large bin.
• If the sample is light, the balance asks for more pieces; add the number shown and press PRINT. lo means the sample is too light to store.
• ACAI improves the unit weight as you add three or more pieces; leave the pan alone while it works.
• The data memory holds up to 50 unit weights, so a parts room can recall each part number instead of re-sampling.
• For counting-only stations, see our counting scale buying guide.

Percent, hold, accumulation and the comparator

• Percent: press MODE to the percent display, press SAMPLE, press RE-ZERO, place the reference (10 g or more) and press PRINT.
• Animal hold: the hold function steadies and holds the reading of a moving load, such as an animal. Pair it with the GP-12 animal pan (not included).
• Accumulation: adds weighings to a running total for batches; turn it on in the function table with data memory set to 0.
• Comparator: HI, OK and LO indicators check fills and kits against limits you store. The GP-04 board (not included) adds HI, OK and LO relay outputs and a buzzer.

Weighing below the balance with the under-hook

The GP-20K uses a strong magnet inside its sensor, so A&D recommends weighing iron and steel parts hung below the balance, away from the magnet. The A&D GP-20 under-hook (OP-20 in the manual; not included) fits the GP-12K, GP-20K, GP-30K, GP-32K and GP-40K. It is also used for density work, such as concrete coarse aggregate. Stand the balance on a frame or a table with an opening so the load hangs freely.

RS-232C, GLP reports and PC software

• The GP-20K is a DCE device; connect it to a PC with a straight-through RS-232C cable (not included).
• WinCT, A&D’s Windows communication tools, reads weights into a PC or spreadsheet.
• Set dout to add GLP output, and each calibration prints or stores a report with the time and date from the built-in clock. Data memory holds up to 50 calibration and calibration test records.
• The GP-06 board (not included) adds an analog voltage output and replaces the standard RS-232C port. See connecting a scale to a computer by USB or RS-232.

Washdown care for an IP65 balance

• IP65 means dust-tight and protected against water jets, so you can wash the GP-20K with water.
• Clean with a lint-free cloth and warm water with a mild detergent; skip organic solvents.
• IP65 covers water jets; keep the balance out of soak tanks and away from pooled water.
• Press ON:OFF and wait for zero before you unplug the adapter, so the internal mass is parked.
• Our washdown scales guide compares IP65, IP67 and IP69K ratings.

GP-20K error codes

Display / code	Meaning	What to do
EC, E11	Stability error	Stop vibration, drafts, temperature swings, static and magnetic fields; press CAL
EC, E16	Internal mass gave the wrong change	Clear the pan and start again
EC, E17	Internal mass mechanism fault	Start again; call us if it repeats
EC, E20	Calibration weight too heavy	Check the weight and the value set; press CAL
EC, E21	Calibration weight too light	Check the weight and the value set; press CAL
CH ng (CHECK NG)	Response adjustment could not settle	Check drafts, vibration, magnetic fields and the pan; press CAL
CH no (CHECK NO)	Internal error found by the self check	Send it for repair
EC, E00 to E07	RS-232C command and format errors	Check baud rate, parity, format and the command sent

An overload message means the load is over capacity; remove it. If a code returns after a power cycle with an empty pan, send the balance to our repair bench. Other brands’ codes are in our scale error codes guide, and drifting readings in scale will not zero or keeps drifting.

GP-20K calibration: built-in mass, 10 kg or 20 kg external weight

The GP-20K calibrates with its internal mass plus an external weight: automatic self calibration when it senses a temperature change, one-touch calibration with the built-in mass, and calibration with an external 10 kg or 20 kg weight. A&D calls for calibration at first install, after a move, when the room changes and on a regular schedule. Our internal vs external calibration guide explains the difference.

One-touch calibration with the internal mass

1. Warm up for at least 30 minutes with nothing on the pan.
2. Press CAL. The balance shows Calin and weighs its internal mass; keep drafts and bumps away.
3. When end appears, it returns to weighing (and prints or stores a GLP report if dout is set for it).

Keep the pan clear when the balance is idle: automatic self calibration only runs with an empty pan, and it runs even in standby.

Calibration with a 10 kg or 20 kg external weight

1. Warm up for at least 30 minutes with nothing on the pan.
2. Hold CAL until Calout appears, then release; the display shows Cal 0.
3. To change the weight value, press SAMPLE: RE-ZERO picks 10 kg or 20 kg or adjusts the last digits, and PRINT stores it. The value stays in memory after power-off.
4. With the pan empty, press PRINT to weigh zero.
5. Place the displayed weight in the center of the pan and press PRINT. When end appears, remove the weight.
6. Put the weight back on and confirm the reading is within 2 digits of its value; if not, check for drafts and vibration and repeat.

For a check without changing calibration, hold CAL until CCout appears to run a calibration test (GLP output must be on). The internal mass can drift with age or corrosion, so check it against a 20 kg external weight on a schedule; A&D’s correction routine (C5in) trims it by up to 5.0 g. Our calibration weight classes guide explains which class suits a 0.1 g balance, we stock calibration weights, and our how often should a scale be calibrated guide helps set a schedule.

GP-20K vs GP-30KS, GP-32K and GP-102K

Model (our listing)	Capacity x readability	Repeatability	Linearity	Display
GP-20K	21 kg x 0.1 g	0.1 g	±0.2 g	Swing arm
GP-30KS	31 kg x 0.1 g	0.1 g	±0.2 g	Separate, 3 m cable
GP-32K	31 kg x 1 g, with a 6 kg x 0.1 g precision range	0.5 g / 0.1 g	±1 g / ±0.2 g	Swing arm
GP-102K	101 kg x 10 g, with a 61 kg x 1 g precision range	5 g / 1 g	±10 g / ±2 g	Swing arm

Pick the GP-20K when 21 kg covers your heaviest container plus load and you want 0.1 g across the whole range. The GP-30KS gives 31 kg at 0.1 g with the display on a cable for washdown lines. The GP-32K and GP-102K use A&D’s smart range, which keeps the fine step even with a heavy tare on the pan.

Selling by weight: choose an NTEP FG-K bench scale

The GP-20K is built for production, lab, packing and washdown weighing at 0.1 g. For trade use, A&D’s FG Series holds NTEP Certificate of Conformance 05-101A1, listed as Active, Class III, on NCWM’s certificate search on November 1, 2026. For selling by weight up to 60 lb, choose the NTEP A&D FG-30KBMN (60 lb x 0.02 lb); our FG-60KBM manual guide covers the FG-K family. Our what is NTEP guide explains the approval, and our free legal-for-trade scale checker helps decide whether your use is trade.

Texas note: TDA does not require an NTEP certificate for every device, but the scale must meet NIST Handbook 44 and suit its use; some scales do need one, so we recommend NTEP models and can check yours. See TDA’s scales used in trade guidance (PDF) and our TDA scale certification guide, or call us or TDA to confirm your use.

Who uses the GP-20K

• Food and meat processing: batching and portion checks in rooms that get hosed down.
• Chemicals, coatings and plastics: formulation and pigment batches up to 21 kg in 0.1 g steps.
• Labs and aggregate testing: large samples, and density work on the under-hook.
• Manufacturing and kitting: counting parts and checking kits with HI/OK/LO limits.
• Animal research and veterinary work: the hold function with the GP-12 animal pan.

Setup tips from our technicians

• Our TDA-registered technicians give a GP-20K the full 12-hour warm-up after delivery before the first calibration.
• Leave it plugged in with the pan clear overnight so automatic self calibration can keep up with the room.
• Run the MODE-key response adjustment once in its final spot; it sets FAST, MID. or SLOW for that bench.
• Hang steel parts on the under-hook instead of setting them on the pan near the sensor magnet.
• Lock the calibration switches once it is set up, so only your QA lead can recalibrate.

Common mistakes we see

• Unplugging the adapter while the internal mass is moving; press ON:OFF and wait for zero first.
• Calibrating minutes after a move, before the balance has reached room temperature.
• Leaving a bin on the pan overnight, which stops automatic self calibration.
• Pressure-washing the balance like an IP69K scale, or letting it sit in standing water.
• Calibrating with a weight that differs from the value set at Cal 0, which ends in E20 or E21.

Browse all A&D precision balances.

Calibration, repair and rentals from MNM Scales

• Book calibration: the GP-20K is in our 6.2 to 35 kg tier: in-house calibration with a certificate is $250 and NIST calibration with a NIST-traceable certificate is $595. See our balance calibration service in Houston, all tiers on the scale calibration service page, and NIST vs in-house certificates.
• Mail-in calibration: remove the pan, pack the balance in its original box and foam, and ship it with the mail-in calibration service.
• Cypress pickup by appointment: drop off or pick up at our Cypress, TX shop (21249 FM 529 Rd, Cypress, TX 77433).
• On-site service: on-site calibration is $295 plus $2 per mile, round trip, once per visit, plus the calibration fee for each scale. Our TDA-registered technicians bring certified test weights to plants, labs, packing rooms and washdown areas across the Houston area.
• Repair: display, keypad, adapter, internal mass and sensor problems go to our scale repair bench.
• Rentals: we rent all types of scales; ask about a scale rental while yours is in for service.

Frequently asked questions

Where can I download the A&D GP-20K manual?

A&D publishes the GP series instruction manual, which covers the GP-20K, as a PDF and on its GP-20K product page. This guide collects the GP-20K numbers from it.

How do I calibrate the GP-20K?

Warm it up for 30 minutes with the pan empty and press CAL. The balance shows Calin, weighs its internal mass and shows end when it is done. To use an external weight, hold CAL until Calout appears.

What weight do I need to calibrate the GP-20K externally?

A&D lists 10 kg and 20 kg as usable calibration weights for the GP-20K. Select the value at Cal 0 with the SAMPLE and RE-ZERO keys, and store it with PRINT.

Does the GP-20K have internal calibration?

Yes, internal mass plus external. It has a built-in calibration mass for one-touch calibration with the CAL key and for automatic self calibration when the room temperature changes, and it also calibrates with an external 10 kg or 20 kg weight.

Can I wash the GP-20K?

Yes. It complies with IP65, dust-tight and protected against water jets. Clean it with warm water and a mild detergent and keep it out of submersion.

How long should the GP-20K warm up?

At least 30 minutes before daily use. After the first install or a move, A&D calls for at least 12 hours and then a calibration.

Is the GP-20K NTEP approved?

No. The GP-20K is non-NTEP. Need it legal for trade? Here is an NTEP alternative: A&D GX-32001LN. For selling by weight up to 60 lb, choose the NTEP Class III A&D FG-30KBMN (CC 05-101A1).

What does EC, E11 mean on the GP-20K?

E11 is a stability error: vibration, drafts, temperature changes, static or a magnetic field keep the reading from settling. Fix the cause and press CAL to return to weighing.