A concrete batching plant runs several weighing loops at once — aggregate, water, cement — and a failed indicator on any of them stops production. This is a field job where one PT650D failed and had to be replaced without rewiring the panel or reprogramming the PLC.
Why indicator choice matters here
Tank weighing systems usually sit in electrically noisy environments. Selecting equipment that stays stable under that interference is the first consideration, ahead of features.
PT650D specification
- Supports 4 load cells at 350 Ω, supply 10 V DC / 150 mA
- Input sensitivity 0.5 to 200 µV/D
- Zero range adjustable from 0.05 mV to 15 mV
- Non-linearity 0.005 % F.S.D.
- A/D conversion rate 200 per second
- Internal resolution 16,700,000
- Capacity setting from 500 to 100,000
- Supply 220 V AC, 50–60 Hz
That combination — high internal resolution with a fast conversion rate and fine input sensitivity — is what makes the PT650D suit batching plant duty.
How the indicator talks to the PLC
The link is an analog 0–10 V signal. The indicator puts out a voltage in that range, the PLC reads it and computes the weight from there.
It is a deliberately simple approach — no protocol to configure, no addressing to lose — and it holds accuracy well enough for batching. That simplicity is also what makes the indicator swappable: any replacement that produces the same 0–10 V output will work with the existing PLC program.
The replacement
Because the plant had to be back in service quickly, the approach was to fit an equivalent indicator rather than repair. The requirements were narrow: matching physical size, and the same analog output. The choice was the Keli XK3101E.
What the changeover involved
1 Fit the XK3101E into the cabinet, reusing the original connector from the PT650D. Nothing in the panel wiring had to change.
2 Enter the indicator settings: capacity, division, then calibrate.
3 Configure the 0–10 V output — principally the voltage at zero and at span, so the PLC reads the same values as before.
Watch the voltage drop at the PLC analog card
The voltage the indicator sends is not necessarily the voltage the card receives. Set the output while measuring at the card input, not at the indicator terminals — otherwise the batch weights come out consistently light or heavy and the cause is hard to find later.
Field service note
KALA Technical Notes
Swapping an indicator on a running plant works when the analog output can be matched exactly. Send us the model that failed and the signal range the PLC expects, and we will confirm which replacement drops into the same connector.
● Weight indicators with analog and digital outputs for batching and process control.