DS4820A1SA | GE Factory Tested & ISO Certified

Description

Product Introduction

You can’t control what you can’t measure, and the DS4820A1SA measures it well. This is GE’s workhorse analog input board for the Mark V system—eight channels of high-accuracy 4-20mA or voltage input, used for everything from fuel gas pressure to steam flow to lube oil temperature. It’s a no-nonsense board that’s been in the field for decades.

Compared to the DS4820A1S (non-A revision), the “A” revision adds a hardware upgrade to the input filter—the new design improves 50/60 Hz common-mode rejection from 90 dB to 100 dB, which matters in plants with heavy electrical noise. The terminal assignment is identical—direct drop-in. No firmware changes required.

Key Technical Specifications

Compatible Replacement Models

Frequently Asked Questions (FAQ)

Q: What’s the difference between the A1SA and the A1S?
The A1SA has an improved analog input filter for better common-mode rejection (100 dB vs. 90 dB). If you have a lot of 50/60 Hz noise in your plant (e.g., from large motors or VFDs), the A1SA will give you cleaner readings. The component-level change also improves the board’s long-term stability—field data shows about half the drift per year compared to the A1S (0.01% vs. 0.02% over 5 years).

Q: How do I wire a 2-wire 4-20mA transmitter to the A1SA?
A 2-wire loop-powered transmitter needs an external 24V supply—the A1SA doesn’t provide loop power. Connect the 24V supply’s positive terminal to the transmitter’s positive terminal. Connect the transmitter’s negative terminal to the board’s Input+ (channel positive). Connect the board’s Input- (channel negative) back to the 24V supply’s 0V terminal. The board’s internal 250Ω resistor creates the voltage drop. Use shielded twisted-pair cable and ground the shield at the supply end only.

Q: The input reading is noisy. What’s the first thing to check?
Ground loops. The A1SA has differential inputs, but if the transmitter and the Mark V rack have different earth potentials, you’ll see AC noise on the reading. Measure the AC voltage between the transmitter’s 0V and the rack’s 0V—if it’s above 0.5V AC, install a signal isolator. Also check if you’re using the correct shield grounding—the shield should be grounded at the transmitter end, not at the rack. If the shield is grounded at both ends, it creates a ground loop.

Q: What’s the maximum cable length for 4-20mA inputs?
GE specifies 300 meters (1000 ft) for 4-20mA loops with 18 AWG wire. At 20mA, the voltage drop in the cable is about 0.6V per 100 meters. The A1SA’s input requires at least 2V across the 250Ω burden resistor (that’s 8mA minimum). If the transmitter can’t deliver enough voltage due to cable drop, the current will saturate below 4mA. For long runs, use a transmitter with a higher compliance voltage or reduce the cable resistance with thicker wire.

Q: The Fault LED is solid red on power-up. What’s the most common cause?
A solid red Fault LED on the A1SA usually indicates a power supply issue—the 24V backplane voltage is below 18V. Check the rack’s 24V supply. If the voltage is fine, the board’s internal DC-DC converter may have failed. Try the board in a known-good slot. If the fault follows the board, it’s likely a hardware failure. If it stays in the same slot, the backplane may have a problem.

Q: Can I mix current and voltage inputs on the same board?
Yes—the A1SA has software-selectable ranges per channel. Channels 1-4 could be 4-20mA, channels 5-8 could be 0-10V. The board will automatically switch the burden resistor in/out based on the configuration. Make sure your field wiring matches the configuration—a 4-20mA transmitter on a channel configured for 0-10V will read near zero (the transmitter will be trying to drive current into a 1MΩ load, which won’t work).

Q: What’s the input sample rate and how does it affect my control loop?
The A1SA samples all 8 channels at 50 Hz (20ms update rate). That’s fast enough for most turbine control loops (pressure, temperature, flow). If you need faster response (e.g., for surge control), you might need a dedicated high-speed module. The sample rate is fixed—you can’t change it.

Q: Does the A1SA support HART communication?
No—the A1SA doesn’t have a HART modem. It reads the analog current and ignores the HART FSK signal (the ~1 kHz frequency shift keying is filtered out). If you need HART communication, you’ll need a separate HART multiplexer or a dedicated HART input module. The A1SA will read the 4-20mA signal from a HART transmitter just fine, but you won’t be able to configure the transmitter or read its diagnostics through this board.

Q: What’s the insulation resistance test value for a pass?
We test every A1SA at 500V DC between the input terminals and the backplane/chassis ground. The minimum is 10 MΩ. Most units measure 50-100 MΩ out of the box. If you see below 5 MΩ, the board may have moisture ingress or contamination—common in coastal or humid environments. The conformal coating on the A1SA is rated for high humidity, but if the board is stored improperly, the coating can degrade. Contact us for inspection.

Q: Can I hot-swap the A1SA while the turbine is running?
The backplane supports live insertion, but we don’t recommend it for analog input boards. Pulling a board breaks the current loops to field transmitters—the CPU will see open-loop faults and might trip alarms. Also, inserting a board while the transmitters are live can cause a momentary current spike. For critical applications, schedule a planned outage or at least put the turbine in a stable idle state.

Q: What’s the lead time for a surplus A1SA?
We keep 5-8 units in stock. Domestic: 2-3 business days ground, overnight if ordered by 2 PM EST. International: 5-7 days via DHL, with customs potentially adding 1-3 days. This board is not ITAR-controlled, so we can ship to most countries without an export license. We include a GE certificate of origin and commercial invoice with every shipment. If you need expedited shipping for a critical outage, contact us directly.

ABB HIEE401782R0001/LTC391AE01
A-B 22C-D072A103
KUKA DSE-IBSC33-1.40
Hollysys FM146B